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/quality-checks-csharp.md

@@ -30,7 +30,7 @@ jobs:
 | `working-directory` | `.` | Directory, relative to the repository root, whose files are checked |
 | `project` | empty | Solution or project file, relative to `working-directory`; empty uses the single `*.sln` or `*.slnx`, else the single `*.csproj`, that is tracked there |
 | `dotnet-sdk-version` | `10.0.401` | Exact version of the .NET SDK, 10 or later; a channel such as `10.0`, a range and a version below 10 are refused |
-| `tools-ref` | `v1` | Tag or branch of `TirSystem/github-action` from which the script `tools/quality-checks-csharp.sh` is fetched |
+| `tools-ref` | `v2` | Tag or branch of `TirSystem/github-action` from which the script `tools/quality-checks-csharp.sh` is fetched |
 
 Reference the workflow at the major tag (`@v1`) or at an exact tag, never at
 `main`. A call at an exact tag is pinned completely only when `tools-ref` names