[main-0.10.x] Skip changelog generation if there is nothing to be viewed

.changelog/current/2464-fix-changelog-checker.md

@@ -0,0 +1,4 @@
+# Fixed
+- Prevent failure of changlog builder when parsing dependabot PRs without explicit changelog stub
+  [backported #2461](https://github.com/nextcloud/cookbook/pull/2461)
+

.github/workflows/pull-checks.yml

@@ -86,13 +86,15 @@ jobs:
                         echo "### No changelog was needed"
                         echo ""
                         echo "No changelog entry was found so far."
-                        echo "This is okay, as no files have been modified that would require a changelog entry."
-                        echo "You might consider if adding a changelog entry would be benefical as significant changes have been made."
+                        echo -n "This is okay, as no files have been modified that would require a changelog entry. "
+                        echo -n "You might consider if adding a changelog entry would be benefical as significant changes have been made. "
+                        echo 'The changelog should be in a file starting with `.changelog/current/${{ github.event.number }}-`.'
                     } > $GITHUB_STEP_SUMMARY
                     fi
                 if: ${{ steps.diff.outputs.num_lines == 0 }}
             -   name: Install Python package
                 run: pip install --user virtualenv pipenv
+                if: ${{ steps.diff.outputs.num_lines != 0 }}
             -   name: Test creation of changelog
                 run: |
                     cd .helpers/changelog
@@ -108,6 +110,7 @@ jobs:
                         python -m changelog_builder --token token --ci --pr ${{ github.event.number }} ../../.changelog/current/* 2>&1
                         echo '```'
                     } >> $GITHUB_STEP_SUMMARY
+                if: ${{ steps.diff.outputs.num_lines != 0 }}
 
     todo-checker:
         name: Check for added todo messages