Upgrade action to v7 and enable signed commits

Author: danbarr

.github/workflows/update-toolhive-reference.yml

@@ -41,7 +41,7 @@ jobs:
 
       - name: Create Pull Request
         if: steps.git-diff.outputs.changed == 'true'
-        uses: peter-evans/create-pull-request@c5a7806660adbe173f04e3e038b0ccdcd758773c # v6
+        uses: peter-evans/create-pull-request@271a8d0340265f705b14b6d32b9829c1cb33d45e # v7
         with:
           branch: update-toolhive-reference-${{ steps.imports.outputs.version }}
           title: |
@@ -51,3 +51,4 @@ jobs:
           commit-message: |
             Update ToolHive reference docs for ${{ steps.imports.outputs.version }}
           delete-branch: true
+          sign-commits: true