matrix.yml: add ucrt64 to the architecture axis

The manually-triggered `test all artifact flavors` matrix already
covers every flavor on `i686` and `x86_64`. Add `ucrt64` as a third
value in the `architecture` array so the same four flavors get
spawned against it too, replacing the previous one-row `include`
block (which was added when only `flavor: full` worked for `ucrt64`)
and dropping the now-stale comment that justified that asymmetry.

Assisted-by: Opus 4.7
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.github/workflows/matrix.yml

@@ -9,19 +9,12 @@ jobs:
       fail-fast: false
       matrix:
         flavor: ['minimal', 'makepkg-git', 'build-installers', 'full']
-        architecture: ['i686', 'x86_64']
+        architecture: ['i686', 'x86_64', 'ucrt64']
         exclude:
           - flavor: minimal
             architecture: i686
           - flavor: makepkg-git
             architecture: i686
-        # `ucrt64` is wired up end-to-end only for `flavor: full`; the
-        # subset flavors depend on follow-up work in `build-extra` and
-        # the `ci-artifacts` pipeline of `git-sdk-64`. Add the one
-        # combination we can meaningfully exercise.
-        include:
-          - flavor: full
-            architecture: ucrt64
     steps:
       - uses: actions/checkout@v6
       - name: run in-place