Only install MinGW when necessary

Installing MinGW 11 takes way too long to tolerate doing this in
all Windows jobs.

.github/workflows/ci.yml

@@ -105,11 +105,15 @@ jobs:
         max_attempts: 10
         timeout_minutes: 3
         command: |
-          choco uninstall mingw
-          choco install mingw --version 11.2.0
           choco install ninja OpenCppCoverage -y
           echo "C:\Program Files\OpenCppCoverage" >> $env:GITHUB_PATH
 
+    - name: Install MinGW
+      if: matrix.platform.name == 'Windows MinGW'
+      run: |
+        choco uninstall mingw
+        choco install mingw --version 11.2.0
+
     - name: Configure CMake
       shell: bash
       run: cmake --preset dev -DCMAKE_VERBOSE_MAKEFILE=ON ${{matrix.platform.flags}} ${{matrix.config.flags}} ${{matrix.type.flags}}