Group permissions not applied to new subgroups or projects
### Summary
When a group `A` is shared with another group `P`(eople), new projects and/or subgroups below `A` will not inherit the permissions automatically.
A workaround is, to change the rights of `P` temporarily (e.g. grant only "Guest" rights and change back to "developer" later). Then new objects are accessible to `P`.
### Steps to reproduce
1. become admin (probably not necessary)
2. create a `/test-toplevel` group
3. go to "Members" -> "Invite Group" and add another group as "Guest" (here: `_groups/embedded`)
<details>
<summary>Screenshot</summary>
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4. create a subgroup "test" and/or a project "test-project"
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<summary>Screenshot</summary>
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5. become some normal user who is member of the `_groups/embedded`
6. visit `/test-toplevel`
### Example Project
### What is the current *bug* behavior?
The "test" subgroup and the "test-project" project are not accessible. Neither directly, nor are they visible in the group tree view.
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<summary>Screenshot (empty group tree view)</summary>
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After changing permissions (from step 3) to "Developer" and then back to "Guest", objects are accessible.
<details>
<summary>Screenshots</summary>
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2. 
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### What is the expected *correct* behavior?
Subgroups + Projects should be visible without changing permissions temporarily.
### Relevant logs and/or screenshots
### Output of checks
#### Results of GitLab environment info
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<summary>Expand for output related to GitLab environment info</summary>
<pre>
System information
System:
Current User: git
Using RVM: no
Ruby Version: 2.6.5p114
Gem Version: 2.7.10
Bundler Version:1.17.3
Rake Version: 12.3.3
Redis Version: 5.0.7
Git Version: 2.24.1
Sidekiq Version:5.2.7
Go Version: unknown
GitLab information
Version: 12.9.2
Revision: ac5568eb5d8
Directory: /opt/gitlab/embedded/service/gitlab-rails
DB Adapter: PostgreSQL
DB Version: 9.6.10
URL: https://gitlab.intern.sigma-chemnitz.de
HTTP Clone URL: https://gitlab.intern.sigma-chemnitz.de/some-group/some-project.git
SSH Clone URL: git@gitlab.intern.sigma-chemnitz.de:some-group/some-project.git
Using LDAP: no
Using Omniauth: yes
Omniauth Providers:
GitLab Shell
Version: 12.0.0
Repository storage paths:
- default: /srv/git-data/repositories
GitLab Shell path: /opt/gitlab/embedded/service/gitlab-shell
Git: /opt/gitlab/embedded/bin/git
</pre>
</details>
#### Results of GitLab application Check
<details>
<summary>Expand for output related to the GitLab application check</summary>
<pre>
everything green except
Init.d configured correctly? ... skipped
MailRoom running? ... skipped
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
</pre>
</details>
### Possible fixes
issue