chore: modify _update-self-references workflow to use a PAT

[FidelusAleksander]

Changes

Built in secrets.GITHUB_TOKEN does not have permissions to commit to .github/workflows directory even with contents: write permission.
The permission workflows: write is needed, which can't be granted through the permission block. See peter-evans/create-pull-request#3558

• .github/workflows/_update-self-references.yml: Added comments explaining the use of a Personal Access Token (EXERCISE_TOOLKIT_TOKEN) instead of the default GITHUB_TOKEN to enable commits to workflow files.
• .github/workflows/_update-self-references.yml: Updated the Create Pull Request step to use the EXERCISE_TOOLKIT_TOKEN for authentication.

Pull request configuration updates:

• .github/workflows/_update-self-references.yml: Removed the reviewers field and adjusted the labels field by removing the maintenance label.

Checklist

• I have added or updated appropriate labels to this PR
• I have tested my changes
• I have updated the documentation if needed

[Copilot]

Pull Request Overview

This PR switches the self-references update workflow to use a Personal Access Token for committing changes to workflow files and cleans up reviewer/label settings.

• Adds explanatory comments about using EXERCISE_TOOLKIT_TOKEN PAT
• Updates the Create Pull Request step to use the PAT instead of GITHUB_TOKEN
• Removes the reviewers field and the maintenance label

Comments suppressed due to low confidence (2)

.github/workflows/_update-self-references.yml:43

• [nitpick] The secret name EXERCISE_TOOLKIT_TOKEN could be made more self-documenting by including PAT (e.g. EXERCISE_TOOLKIT_PAT) to clearly indicate it holds a Personal Access Token.

token: ${{ secrets.EXERCISE_TOOLKIT_TOKEN }}

.github/workflows/_update-self-references.yml:5

• To follow least-privilege principles, add an explicit permissions block at the top (e.g., permissions: contents: write, workflows: write) so the workflow doesn’t grant more permissions than necessary.

name: Update Self-References