feat: add useful title and body to check-new-versions.yaml (#615)

### Briefly, what does this PR introduce?
This adds package files to the title, and a diffstat to the body.

### What kind of change does this PR introduce?
- [ ] Bug fix (issue #__)
- [x] New feature (issue #__)
- [ ] Documentation update
- [ ] Other: __

.github/workflows/check-new-versions.yaml

@@ -18,6 +18,7 @@ jobs:
       with:
         path: eic-spack
     - name: Check for new versions and create issue
+      id: new_versions
       env:
         COMMENT_BOT_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       shell: bash
@@ -26,12 +27,17 @@ jobs:
         spack repo add --scope site ${GITHUB_WORKSPACE}/key4hep-spack
         spack repo add --scope site ${GITHUB_WORKSPACE}/eic-spack
         bash eic-spack/.github/scripts/checksum_new_versions.sh
+        echo "files=$(git -C ${GITHUB_WORKSPACE}/eic-spack diff --name-only | xargs -L1 -r dirname | xargs -L1 -r basename | xargs)" >> $GITHUB_OUTPUT
+        echo "diffstat<<EOF" >> $GITHUB_OUTPUT
+        git -C ${GITHUB_WORKSPACE}/eic-spack diff --stat >> $GITHUB_OUTPUT
+        echo "EOF" >> $GITHUB_OUTPUT
     - name: Create pull request
       uses: peter-evans/create-pull-request@v5
       with:
         path: eic-spack
         branch-suffix: short-commit-hash
-        title: New package versions found
+        title: New package versions found for ${{ steps.new_versions.outputs.files }}
         body: |
-          New package versions found
+          New package versions found:
+          ${{ steps.new_versions.outputs.diffstat }}
         assignees: wdconinc