ci : build-msys job slimming [no ci]

This PR attempts to slim down the dependencies for build-msys jobs
making the same changes that we applied in whisper.cpp to reduce the
size of the github actions cache, and should also improve the run time
due to fewer dependencies that need to be installed.

I realize this is a scheduled job but I think it would still make sense
to apply these changes.

Refs: ggml-org/whisper.cpp#3858

Author: danbev

.github/workflows/build-msys.yml

@@ -27,8 +27,8 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - { sys: UCRT64,  env: ucrt-x86_64,  build: Release }
-          - { sys: CLANG64, env: clang-x86_64, build: Release }
+          - { sys: UCRT64,  env: ucrt-x86_64,  compiler: gcc,   build: Release }
+          - { sys: CLANG64, env: clang-x86_64, compiler: clang, build: Release }
 
     steps:
       - name: Clone
@@ -48,9 +48,7 @@ jobs:
           update: true
           msystem: ${{matrix.sys}}
           install: >-
-            base-devel
-            git
-            mingw-w64-${{matrix.env}}-toolchain
+            mingw-w64-${{matrix.env}}-${{matrix.compiler}}
             mingw-w64-${{matrix.env}}-cmake
             mingw-w64-${{matrix.env}}-openblas