workflows: nightly: run on PRs when either workflow or check_versions.py is modified

Run the nightly workflow on PRs when appropriate, but do a dry-run
(i.e. don't actually try creating PRs) in this case so we don't open
things during testing.

AI-Generated: Uses Claude Sonnet 5

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>

Author: threexc

.github/workflows/nightly.yml

@@ -7,6 +7,10 @@ on:
   schedule:
     - cron: '0 2 * * *'
   workflow_dispatch:
+  pull_request:
+    paths:
+      - '.github/workflows/nightly.yml'
+      - 'ci_scripts/check_versions.py'
 
 permissions:
   contents: write
@@ -35,7 +39,7 @@ jobs:
       - name: Check versions and open PRs
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: python3 ci_scripts/check_versions.py --summary --create-prs
+        run: python3 ci_scripts/check_versions.py --summary${{ github.event_name != 'pull_request' && ' --create-prs' || '' }}
 
   check_deprecated_packages:
     runs-on: ubuntu-latest