Adjust demo-dataset for CI (#12500)

.github/workflows/frontend.yaml

@@ -33,6 +33,10 @@ env:
   INVENTREE_BACKUP_DIR: /home/runner/work/InvenTree/test_inventree_backup
   INVENTREE_SITE_URL: http://localhost:8000
 
+  # Use the same-named branch of the demo dataset as the target branch of this build,
+  # so that stable branches are not broken by changes to the demo dataset on main
+  DEMO_DATASET_BRANCH: ${{ github.event_name == 'pull_request' && github.base_ref || github.ref_name }}
+
 permissions:
   contents: read
 
@@ -136,7 +140,7 @@ jobs:
           pip-dependency: psycopg2
       - name: Set up test data
         run: |
-          invoke dev.setup-test -iv
+          invoke dev.setup-test -iv --branch "$DEMO_DATASET_BRANCH"
           invoke int.rebuild-thumbnails
       - name: Install dependencies
         run: invoke int.frontend-compile --extract
@@ -218,7 +222,7 @@ jobs:
           pip-dependency: psycopg2
       - name: Set up test data
         run: |
-          invoke dev.setup-test -iv
+          invoke dev.setup-test -iv --branch "$DEMO_DATASET_BRANCH"
           invoke int.rebuild-thumbnails
       - name: Install dependencies
         run: invoke int.frontend-compile --extract