fix: add repository-projects read permission to post-dependabot workflow

[shmsr]

Proposed commit message

Fixes "Resource not accessible by integration (organization.teams)" error when adding team reviewers to dependabot PRs with gh cli

See: cli/cli#6274 (comment) and cli/cli#6274 (comment)
See: https://github.com/orgs/community/discussions/113519

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

[github-actions]

🤖 GitHub comments

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Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @shmsr? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[v1v]

💯
I recall we faced a similar issue in the past:

• https://github.com/elastic/oblt-actions/blob/5aafe09fc821fa7a6b4ac34fdf2e347a43b754ac/mergify/labels-copier/README.md?plain=1#L44-L45