gitlab-ci: Install g++-mingw-w64-x86-64-win32 instead of mingw-w64

mingw-w64 pulls in a lot more packages we don't need.

g++-mingw-w64-x86-64-win32 is only available in Debian testing, so get
all mingw packages from there.

Acked-by: Andres Gomez <agomez@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4851>

.gitlab-ci/container/x86_build.sh

@@ -121,11 +121,6 @@ done
 apt-get install -y --no-remove -t buster-backports \
       llvm-8-dev \
 
-# for 64bit windows cross-builds
-apt-get install -y --no-remove \
-      libz-mingw-w64-dev \
-      mingw-w64
-
 
 # Install packages we need from Debian testing last, to avoid pulling in more
 
@@ -136,6 +131,8 @@ apt-get install -y -t testing \
       libstdc++6:s390x
 
 apt-get install -y --no-remove -t testing \
+      g++-mingw-w64-x86-64-win32 \
+      libz-mingw-w64-dev \
       wine \
       wine32 \
       wine64