fixup! CI: add a GHA for doing a basic build test

Since we're building in a minimal MSYS2 environment, `git` is not
available (at least not MSYS2's) and therefore the `configure` log would
show this:

  /d/a/msys2-runtime/msys2-runtime/winsup/configure: line 6858: git: command not found
  configure: WARNING: Could not determine msys2-runtime commit"

Let's work around this by using the `--with-msys2-runtime-commit` route.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/build.yaml

@@ -24,7 +24,7 @@ jobs:
           # resulting in errors due to -Werror. Disable them for now.
           export CXXFLAGS="-Wno-error=stringop-truncation -Wno-error=array-bounds -Wno-error=overloaded-virtual -Wno-narrowing -Wno-use-after-free -Wno-error=maybe-uninitialized"
           (cd winsup && ./autogen.sh)
-          ./configure --disable-dependency-tracking
+          ./configure --disable-dependency-tracking --with-msys2-runtime-commit=$GITHUB_SHA
           make -j8
 
       - name: Install