Fix PR review reminder DAG for case where base branch is 2+ levels deep

[AetherUnbound]

Description

This PR fixes the PR review reminder DAG for the case where a PR depends on a PR 3 levels from main (creating a chain of branch_beyond -> branch_tertiary -> branch_secondary -> main). This case can be seen (at the current time) in #3162 which depends on #3161 which depends on #3143 which is pointed at main. For some reason, that many levels out from main, there's still some branch protection information but nothing which has the required pull request reviews.

Testing Instructions

Run the PR review request reminder DAG locally and see that it succeeds (whereas current runs on main are failing).

Tests should also pass!

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.
• I ran the DAG documentation generator (if applicable).

Developer Certificate of Origin

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[krysal]

LGTM. What an odd case!

[stacimc]

LGTM 🤯