[MNT] Delete outdated add_pr2project.yml

[alyssadai]

• Related to Remove outdated add_pr2project.yml from repos workflows#119

FYI: The best way to find all instances of a file across all repos / files using an outdated PAT (e.g., NB_PROJECT_PAT) is using the search bar in https://github.com/neurobagel. Did not think of that the first time around when addressing neurobagel/workflows#119.... 🙈

Checklist

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• PR has an interpretable title with a prefix ([ENH], [FIX], [REF], [TST], [CI], [MNT], [INF], [MODEL], [DOC]) (see our Contributing Guidelines for more info)
• PR links to GitHub issue with mention Closes #XXXX
• Tests pass
• Checks pass

For new features:

• Tests have been added

For bug fixes:

• There is at least one test that would fail under the original bug conditions.

[surchs]

🎉

🧑‍🍳