No mail notification sent for group access request
### Summary
When a user requests access to a Gitlab group with the "Request Access" link on the Group overview page, there is no notification mail triggered to the group owners.
### Steps to reproduce
Create a new group with with User A and request access to the group with User B.
### What is the current *bug* behavior?
We can observe this behavior with two different Gitlab Versions (13.3.6-ee and 13.4.2-ee).
Within `gitlab-rails/production.log` we can see the following:
```
[ActiveJob] Enqueued ActionMailer::MailDeliveryJob (Job ID: bd81d0ce-d578-4bf0-84e9-436991c085fb) to Sidekiq(mailers) with arguments: "Notify", "member_access_requested_email", "deliver_now", {:args=>["Group", 77, 2]}
[ActiveJob] [ActionMailer::MailDeliveryJob] [bd81d0ce-d578-4bf0-84e9-436991c085fb] Performing ActionMailer::MailDeliveryJob (Job ID: bd81d0ce-d578-4bf0-84e9-436991c085fb) from Sidekiq(mailers) enqueued at 2020-10-05T13:24:08Z with argument
s: "Notify", "member_access_requested_email", "deliver_now", {:args=>["Group", 77, 2]}
[ActiveJob] [ActionMailer::MailDeliveryJob] [bd81d0ce-d578-4bf0-84e9-436991c085fb] Performed ActionMailer::MailDeliveryJob (Job ID: bd81d0ce-d578-4bf0-84e9-436991c085fb) from Sidekiq(mailers) in 2.89ms
```
From Gitlab perspective this looks like everything is ok, but there is no mail dispatched to either sendmail or smtp (depening on the configuration).
**The interesting note** is, that notifications from Gitlab in general work fine (e.g. access request for projects, pipeline failures). We only can notice this with group access requests.
### What is the expected *correct* behavior?
When a user requests access to a group, there should be a mail dispatched to the group owner.
### Relevant logs and/or screenshots
<!-- Paste any relevant logs - please use code blocks (```) to format console output, logs, and code
as it's tough to read otherwise. -->
#### Results of GitLab environment info
Gitlab Omnibus installation on CentOS 7.8, Gitlab 13.3.6-ee and 13.4.2-ee
<details>
<summary>Expand for output related to GitLab environment info</summary>
<pre>
(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)
System information
System:
Proxy: no
Current User: git
Using RVM: no
Ruby Version: 2.6.6p146
Gem Version: 2.7.10
Bundler Version:1.17.3
Rake Version: 12.3.3
Redis Version: 5.0.9
Git Version: 2.28.0
Sidekiq Version:5.2.9
Go Version: unknown
GitLab information
Version: 13.3.6-ee
Revision: d7bc82f4b06
Directory: /opt/gitlab/embedded/service/gitlab-rails
DB Adapter: PostgreSQL
DB Version: 11.7
URL: http://gitlab.example.com
HTTP Clone URL: http://gitlab.example.com/some-group/some-project.git
SSH Clone URL: git@gitlab.example.com:some-group/some-project.git
Elasticsearch: no
Geo: no
Using LDAP: no
Using Omniauth: yes
Omniauth Providers:
GitLab Shell
Version: 13.6.0
Repository storage paths:
- default: /var/opt/gitlab/git-data/repositories
GitLab Shell path: /opt/gitlab/embedded/service/gitlab-shell
Git: /opt/gitlab/embedded/bin/git
(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)
</pre>
</details>
#### Results of GitLab application Check
<!-- Input any relevant GitLab application check information if needed. -->
<details>
<summary>Expand for output related to the GitLab application check</summary>
<pre>
(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:check SANITIZE=true`)
Checking LDAP ... [0/1132]
LDAP: ... LDAP is disabled in config/gitlab.yml
Checking LDAP ... Finished
Checking GitLab App ...
Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ...
2/1 ... yes
14/2 ... yes
6/3 ... yes
3/4 ... yes
20/5 ... yes
7/6 ... yes
22/7 ... yes
23/8 ... yes
22/9 ... yes
18/10 ... yes
18/11 ... yes
22/12 ... yes
24/13 ... yes
26/14 ... yes
33/15 ... yes
35/16 ... yes
36/17 ... yes
37/18 ... yes
38/19 ... yes
39/20 ... yes
40/21 ... yes
41/22 ... yes
2/23 ... yes
18/24 ... yes
Redis version >= 4.0.0? ... yes
Ruby version >= 2.5.3 ? ... yes (2.6.6)
Git version >= 2.24.0 ? ... yes (2.28.0)
Git user has default SSH configuration? ... yes
Active users: ... 17
Is authorized keys file accessible? ... yes
GitLab configured to store new projects in hashed storage? ... yes
All projects are in hashed storage? ... yes
Elasticsearch version 6.x - 7.x? ... skipped (elasticsearch is disabled)
Checking GitLab App ... Finished
Checking GitLab subtasks ... Finished
(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true`)
(we will only investigate if the tests are passing)
</pre>
</details>
### Possible fixes
<!-- If you can, link to the line of code that might be responsible for the problem. -->
issue