Sentry connection is not updating projects list
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### Summary
<!-- Summarize the bug encountered concisely. -->
When trying to link GitLab monitoring to a Sentry project, once the connection is established, the projects list dropdown does not seem to be updated.
### Steps to reproduce
<!-- Describe how one can reproduce the issue - this is very important. Please use an ordered list. -->
- Create a GitLab project
- Create a Sentry project (for example on Sentry cloud)
- Try linking the GitLab monitoring service to the Sentry project (in `Settings` > `Monitoring`)
- Create a valid auth token on the Sentry instance
- Enter the Sentry URL
- Enter the Sentry auth token
- Click `Connect`
- See the connection is successful
- **See the projects list dropdown is still disabled with no projects being listed**
### Example Project
<!-- If possible, please create an example project here on GitLab.com that exhibits the problematic
behavior, and link to it here in the bug report. If you are using an older version of GitLab, this
will also determine whether the bug is fixed in a more recent version. -->
Not applicable (private auth token).
### What is the current *bug* behavior?
<!-- Describe what actually happens. -->
The Sentry projects list is empty.
### What is the expected *correct* behavior?
<!-- Describe what you should see instead. -->
The Sentry projects list should contain Sentry projects the auth token have access to once connection linked successfully.
### 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. -->
{width=1038 height=631}
### Output of checks
<!-- If you are reporting a bug on GitLab.com, uncomment below -->
This bug happens on GitLab.com
<!-- and uncomment below if you have /label privileges -->
<!-- /label ~"reproduced on GitLab.com" -->
<!-- or follow up with an issue comment of `@gitlab-bot label ~"reproduced on GitLab.com"` if you do not -->
#### Results of GitLab environment info
<!-- Input any relevant GitLab environment information if needed. -->
<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`)
(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`)
(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>
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### Possible fixes
<!-- If you can, link to the line of code that might be responsible for the problem. -->
<!-- If you don't have /label privileges, follow up with an issue comment of `@gitlab-bot label ~"type::bug"` -->
issue