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

.gitea/workflows/quality-checks-cpp.yml

@@ -36,7 +36,7 @@ on:
       tools-ref:
         description: "Tag or branch of TirSystem/github-action whose tools/quality-checks-cpp.sh is run; pin it to the exact tag together with the workflow"
         type: string
-        default: "v1"
+        default: "v2"
 
 jobs:
   quality-checks-cpp: