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

guides/code-metrics.md

@@ -34,7 +34,7 @@ jobs:
     needs: tests
     permissions:
       contents: write
-    uses: TirSystem/github-action/.gitea/workflows/code-metrics.yml@v1
+    uses: TirSystem/github-action/.gitea/workflows/code-metrics.yml@v2
     with:
       coverage-artifact: coverage
       coverage-report: coverage.xml
@@ -49,9 +49,9 @@ jobs:
 | `coverage-warn` | `60` | Coverage in percent below which the badge is red |
 | `coverage-good` | `80` | Coverage in percent from which the badge is green; in between it is yellow |
 | `badges-branch` | `badges` | Branch that holds the badge files; it is created when it does not exist |
-| `tools-ref` | `v1` | Tag or branch of `TirSystem/github-action` from which the scripts in `tools/` are fetched |
+| `tools-ref` | `v2` | Tag or branch of `TirSystem/github-action` from which the scripts in `tools/` are fetched |
 
-Reference the workflow at the major tag (`@v1`) or at an exact tag, never at
+Reference the workflow at the major tag (`@v2`) or at an exact tag, never at
 `main`. A call at an exact tag is pinned completely only when `tools-ref` names
 the same tag. See the upgrade guide. Start the workflow on pushes to your
 default branch only: the badge commit carries `[skip ci]` and is made with the