CI: Fix MinGW install error by pinning to earlier version

Works around egor-tensin/setup-mingw#14.

(cherry picked from commit 0369f6f)

Author: akien-mga

.github/workflows/ci.yml

@@ -104,6 +104,8 @@ jobs:
       - name: Setup MinGW for Windows/MinGW build
         if: ${{ matrix.platform == 'windows' && matrix.flags == 'use_mingw=yes' }}
         uses: egor-tensin/setup-mingw@v2
+        with:
+          version: 12.2.0
 
       - name: Generate godot-cpp sources only
         run: |