MIL-011 tasks 2 to 4: the default tools-ref is the current major

code-metrics.yml defaulted tools-ref to v1 and its guide said @v1, but
the workflow and its scripts exist only from v2.1.0. The default of the
five reusable workflows is now the current major, defined once in
MAJOR_TAG, and tests/test_tools_ref.py fails when a default differs from
it or names a tag without the script. Guides, README and wiki (en, da,
ms) call code-metrics.yml at @v2; ADR-0005, 0008, 0009 and 0010 carry
an amendment; RC-077 accepts the milestone's task 1 results.

Task: MIL-011#2

tests/test_quality_workflow.py

@@ -46,7 +46,7 @@ class TestDefinition:
         }
         assert inputs["languages"]["default"] == "python,shell"
         assert inputs["working-directory"]["default"] == "."
-        assert inputs["tools-ref"]["default"] == "v1"
+        assert inputs["tools-ref"]["default"] == (REPO_ROOT / "MAJOR_TAG").read_text(encoding="utf-8").strip()
 
     def test_tool_versions_are_pinned_to_the_adr(self, document):
         inputs = document[True]["workflow_call"]["inputs"]