refactor: Update test label mapping to load test discovery dynamically

Revised the import mechanism for the test discovery module to load it dynamically by file path, avoiding eager loading of the `dispatcharr` package. This change ensures that the script can run in a bare Python environment before the application virtual environment is set up, improving compatibility with CI processes.

scripts/ci_backend_test_labels.py

@@ -1,17 +1,40 @@
 #!/usr/bin/env python3
-"""Map changed repository paths to Django test package labels for CI."""
+"""Map changed repository paths to Django test package labels for CI.
+
+Loads ``dispatcharr/test_discovery.py`` by file path so this script does not
+import the ``dispatcharr`` package (which eagerly loads Celery). The label step
+runs on the bare runner Python before the app venv exists.
+"""
 
 from __future__ import annotations
 
+import importlib.util
 import json
 import os
 import sys
 from pathlib import Path
 
 REPO_ROOT = Path(__file__).resolve().parent.parent
-sys.path.insert(0, str(REPO_ROOT))
 
-from dispatcharr.test_discovery import labels_for_changed_paths  # noqa: E402
+
+def _load_test_discovery():
+    path = REPO_ROOT / "dispatcharr" / "test_discovery.py"
+    spec = importlib.util.spec_from_file_location(
+        "dispatcharr_test_discovery",
+        path,
+    )
+    if spec is None or spec.loader is None:
+        raise ImportError(f"Unable to load test discovery module from {path}")
+    module = importlib.util.module_from_spec(spec)
+    # Register before exec so dataclasses/typing edge cases that re-import
+    # the module name still resolve.
+    sys.modules[spec.name] = module
+    spec.loader.exec_module(module)
+    return module
+
+
+_test_discovery = _load_test_discovery()
+labels_for_changed_paths = _test_discovery.labels_for_changed_paths
 
 
 def _read_paths(argv: list[str]) -> list[str]: