small updates to action (#79)

* don't self-trigger

* don't open multiple PRs

Author: sbfnk

.github/workflows/render-report.yaml

@@ -9,6 +9,9 @@ on:
   push:
     branches:
       - main
+    paths-ignore:
+      - "**.pdf"
+
 jobs:
   render-report:
     runs-on: macos-latest
@@ -44,7 +47,7 @@ jobs:
           commit-message: "Update rendered report"
           title: "Update rendered report"
           body: "This is an automated pull request to update the rendered report."
-          branch: "render-report-${{ github.run_number }}"
+          branch: "render-report-update"
           labels: "documentation"
           add-paths: |
             report/results.pdf