Enable danger review for forks

What does this MR do?

Due to some limitations Danger bot wasn't enabled repositories which did not set envvar DANGER_GITLAB_API_TOKEN in the CI pipeline which is true for forks e.g. Community contributions. This envvar is needed so Danger bot can comment its results on the MR.

This MR allows Danger bot to be run on forks so Community contributions get early feedback on e.g. git commit messages.

See !57102 (closed) for a fork MR.

Verification

• MR from fork
  • [-] CI should pass/fail depending on the validity of e.g. git commit message
    • CI will always pass due to !57097 (comment 541288558)
  • Does not post results to MR
• MR on GitLab repository/GitLab member triggers pipeline on MR from fork - same
  • CI should pass/fail depending on the validity of e.g. git commit message
  • Does post results to MR

Caveat ⚠

Danger won't fail the CI job even if it on git commit errors. See !57097 (comment 541288558) on the why.

Screenshots (strongly suggested)

Type	With $DANGER_GITLAB_API_TOKEN (this MR)	No $DANGER_GITLAB_API_TOKEN (fork MR)	👈 When CI triggered by GitLab member on MR fork
Danger success ✔	https://gitlab.com/gitlab-org/gitlab/-/jobs/1142903869	https://gitlab.com/rettalps/gitlab/-/jobs/1142906200	https://gitlab.com/gitlab-org/gitlab/-/jobs/1142968956
Comment on MR for ✔		No comment on MR from GitLab 🤖
Danger failure 🚫	https://gitlab.com/gitlab-org/gitlab/-/jobs/1142939345	https://gitlab.com/rettalps/gitlab/-/jobs/1143018598	https://gitlab.com/gitlab-org/gitlab/-/jobs/1142983337
Comment on MR for 🚫		No comment on MR from GitLab 🤖

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • [-] I have included a changelog entry.
  • I have not included a changelog entry because it's developer-facing.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content