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_code_metrics.py

@@ -44,7 +44,7 @@ class TestDefinition:
             "coverage-warn": "60",
             "coverage-good": "80",
             "badges-branch": "badges",
-            "tools-ref": "v1",
+            "tools-ref": (WORKFLOW.parent.parent.parent / "MAJOR_TAG").read_text(encoding="utf-8").strip(),
         }
 
     def test_asks_for_contents_write_and_nothing_else_and_needs_no_secret(self, document):