build-and-deploy: support UCRT64 via the pseudo architecture ucrt64

In git-for-windows/build-extra#711 I am
preparing the `git-extra` package for the MINGW64 -> UCRT64 migration.
Once that lands, the natural next step is to actually build the UCRT64
variants of the affected packages via this workflow, and for that the
workflow has to know about UCRT64.

The `setup-git-for-windows-sdk` action already accepts `ucrt64` as a
value for its `architecture` input (which installs the UCRT64 variant
of git-sdk-64), so let's reuse the same spelling as a pseudo
architecture here: the runner is still `windows-latest` (UCRT64 is
just an alternative MSYS2 environment on x86_64), `git.exe` is looked
up under `/ucrt64/bin/`, and `MINGW_ARCH=ucrt64` is passed to
`makepkg-mingw`.

The `BUILD_SRC` flag stays empty, just like for `i686` and `aarch64`,
because building the `.src.tar.gz` for the x86_64 variant of a package
(should it also be built) already covers what would otherwise be
produced for ucrt64.

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

Author: dscho

.github/workflows/build-and-deploy.yml

@@ -17,7 +17,7 @@ on:
         description: 'The ref containing the package definition'
         required: true
       architecture:
-        description: 'The architecture to build for (only for MSYS packages and all arm64 builds)'
+        description: 'The architecture to build for (only for MSYS packages, ucrt64 builds, and all arm64 builds)'
         required: false
       actor:
         description: The GitHub user on whose behalf this workflow is run
@@ -232,6 +232,10 @@ jobs:
               GIT_EXE="/mingw32/bin/git.exe"
               BUILD_SRC=
               ;;
+            ucrt64)
+              GIT_EXE="/ucrt64/bin/git.exe"
+              BUILD_SRC=
+              ;;
             *)
               GIT_EXE="/mingw64/bin/git.exe"
               BUILD_SRC="YesPlease"
@@ -251,6 +255,7 @@ jobs:
                     aarch64,*) echo "clangarm64";;
                     x86_64,*) echo "mingw64";;
                     i686,*) echo "mingw32";;
+                    ucrt64,*) echo "ucrt64";;
                     ,mingw-w64-wintoast) echo "mingw32 mingw64 clangarm64";; # We're (cross-)compiling via Visual Studio
                     ,mingw-w64-git-credential-manager) echo "mingw32 mingw64 clangarm64";; # We're downloading the pre-built artifacts for all three platforms
                     ,mingw-w64-git-lfs) echo "mingw32 mingw64 clangarm64";; # We're downloading the pre-built artifacts from Git LFS' official release page