[nrf fromlist] ci: Support standalone anchors for reusability

If we want to reuse a set of files for multiple tags, then allow
defining a standalone anchor and skip processing it.

e.g., below will work now, as the first entry wifi_common will be
ignored

wifi_common: *wifi_common
  - a
  - b

ci_samples_wifi:
  files:
    - c
    - *wifi_common

Upstream PR #: 90028

Signed-off-by: Chaitanya Tata <[email protected]>

Author: krish2718

scripts/ci/test_plan.py

@@ -337,6 +337,10 @@ def find_tags(self):
             tag.exclude = True
             tag.name = t
 
+            if not isinstance(x, dict) or x.get("files") is None:
+                logging.debug(f"Tag {t} is might be a standalone anchor, skipping...")
+                continue
+
             # tag._match_fn(path) tests if the path matches files and/or
             # files-regex
             tag._match_fn = _get_match_fn(x.get("files"), x.get("files-regex"))