fix: dependabot creates multiple changesets

[nedsalk]

• closes Dependabot creates duplicate changesets for CI deps #2709

Checklist

• I added — tests to prove my changes
• I updated — all the necessary docs
• I reviewed — the entire PR myself, using the GitHub UI
• I described — all breaking changes and the Migration Guide

[github-actions]

Coverage Report:

Lines	Branches	Functions	Statements
79.62%(+0%)	71.4%(+0%)	77.28%(+0%)	79.71%(+0%)

Changed Files:

Coverage values did not change👌.

[maschad]

I'm okay with these changes, but perhaps we could avoid the repetitive if: env.CHANGESET_FILE == '' checks by doing a check for that as a job, and then having create-changset job dependent on it.

Something like

check-changeset:
    name: Check for Changeset
    runs-on: ubuntu-latest
    outputs:
      changeset_exists: ${{ steps.check_changeset.outputs.exists }}
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0
          ref: ${{ github.event.client_payload.ref }}

      - name: Check for PR's changeset file
        id: check_changeset
        run: |
          CHANGESET_FILE=$(git diff --diff-filter=A --name-only origin/${{ github.base_ref }} .changeset/*.md)
          if [ -z "$CHANGESET_FILE" ]; then
            echo "exists=false" >> $GITHUB_OUTPUT
          else
            echo "exists=true" >> $GITHUB_OUTPUT
          fi

and then the create-changeset would have the conditional

if: github.actor == 'dependabot[bot]' && needs.check-changeset.outputs.changeset_exists == 'false'