chore(gh): switch gh action commit step to an action (janus-idp#2414)

Signed-off-by: Paul Schultz <pschultz@pobox.com>

.changeset/chilled-toys-double.md

@@ -0,0 +1,2 @@
+---
+---

.github/workflows/update-changeset-prs.yaml

@@ -9,19 +9,17 @@ jobs:
   update-and-commit-files:
     name: Update and commit files
     runs-on: ubuntu-latest
+
+    permissions:
+      # Give the default GITHUB_TOKEN write permission to commit and push the changed files back to the repository.
+      contents: write
+
     steps:
       - name: Checkout
         uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4
         with:
-          # don't persist the GITHUB_TOKEN so the release can use use the generated token
-          persist-credentials: false
-
-      - name: Generate token
-        id: generate-token
-        uses: actions/create-github-app-token@31c86eb3b33c9b601a1f60f98dcbfd1d70f379b4 # v1.10.3
-        with:
-          app-id: ${{ vars.JANUS_IDP_GITHUB_APP_ID }}
-          private-key: ${{ secrets.JANUS_IDP_GITHUB_APP_PRIVATE_KEY }}
+          # Fetch the last 2 commits instead of just 1. (Fetching just 1 commit would overwrite the whole history)
+          fetch-depth: 2
 
       - name: Setup Node.js
         uses: actions/setup-node@1e60f620b9541d16bece96c5465dc8ee9832be0b # v4
@@ -33,14 +31,17 @@ jobs:
         # We want to commit the yarn.lock changes
         run: yarn install --no-immutable
 
-      - name: Commit changes
-        env:
-          GITHUB_TOKEN: ${{ steps.generate-token.outputs.token }}
+      - name: Get last commit message
+        id: last-commit
         run: |
-          git config user.name 'janus-idp[bot]'
-          git config user.email '41898282+janus-idp[bot]@users.noreply.github.com'
-          git add yarn.lock
-          if [[ -n $(git status --porcelain) ]]; then
-            git commit -m 'chore: update yarn.lock'
-            git push origin HEAD:${{ github.ref }}
-          fi
+          echo "message=$(git log -1 --pretty=%s)" >> $GITHUB_OUTPUT
+          echo "author=$(git log -1 --pretty=\"%an <%ae>\")" >> $GITHUB_OUTPUT
+
+      - name: Amend previous commit
+        uses: stefanzweifel/git-auto-commit-action@v5
+        with:
+          commit_author: ${{ steps.last-commit.outputs.author }}
+          commit_message: ${{ steps.last-commit.outputs.message }}
+          commit_options: '--amend --no-edit'
+          push_options: '--force'
+          skip_fetch: true