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_workflows_cpp_csharp.py

@@ -68,7 +68,7 @@ class TestDefinition:
             "ref": "${{ inputs.tools-ref }}",
             "path": "shared-scripts",
         }
-        assert inputs_of(workflow)["tools-ref"]["default"] == "v1"
+        assert inputs_of(workflow)["tools-ref"]["default"] == (REPO_ROOT / "MAJOR_TAG").read_text(encoding="utf-8").strip()
 
     def test_inputs_reach_the_script_only_through_the_environment(
         self,