add zink to macos ci

This commit causes zink to be build in the macos ci on every commit.
 In addition to that meson will now error if there is no moltenvk-dir
 given on macos since the build would fail anyways.

 Reviewed-by: Eric Engestrom <eric@igalia.com>
 Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19531>

.github/workflows/macos.yml

@@ -26,6 +26,7 @@ jobs:
         brew "libxcb"
         brew "libxdamage"
         brew "libxext"
+        brew "molten-vk"
         brew "ninja"
         brew "pkg-config"
         brew "python@3.10"
@@ -41,7 +42,7 @@ jobs:
         [binaries]
         llvm-config = '/usr/local/opt/llvm/bin/llvm-config'
         EOL
-        $MESON_EXEC . build --native-file=native_config -Dbuild-tests=true -Dosmesa=true -Dgallium-drivers=swrast -Dglx=${{ matrix.glx_option }}
+        $MESON_EXEC . build --native-file=native_config -Dmoltenvk-dir=$(brew --prefix molten-vk) -Dbuild-tests=true -Dosmesa=true -Dgallium-drivers=swrast,zink -Dglx=${{ matrix.glx_option }}
     - name: Build
       run: $MESON_EXEC compile -C build
     - name: Test