Fix manual trigger

.github/workflows/CI_pytest_weekly.yml

@@ -23,14 +23,15 @@ jobs:
         os: [ubuntu-latest, macos-latest, windows-latest]
 
     steps:
-    # Checkout the master branch from the repository
+    # Checkout the repo
     # The idea for this Action is to spot issues with new dependency versions as soon as they
     # are released (and not when we decide to update ampycloud).
     - name: Checkout current repository
       uses: actions/checkout@v4
       with:
         repository: MeteoSwiss/ampycloud
-        ref: master
+        if: ${{ github.event_name != 'workflow_dispatch' }}
+            ref: master  # If run on schedule, use the master branch.
 
     # Setup python
     - name: Set up Python