Fix 401 errors when installing the GitLab for Jira app

What does this MR do and why?

This backports to 17.5 Fix 401 errors when installing the GitLab for J... (!173110 - merged).

A change in JWT token sent from Atlassian Cloud causes all prior GitLab versions to reject the token when installing the GitLab for Jira Cloud app (a Jira app). This backport changes our validation to match the new format. The fix has been verified on GitLab.com.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:test-on-omnibus-ee job has either succeeded or been approved by a Software Engineer in Test.

Note to the merge request author and maintainer

If you have questions about the patch release process, please:

• Refer to the patch release runbook for engineers and maintainers for guidance.
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