ci: Build mingw image

.github/workflows/mingw.yml

@@ -0,0 +1,24 @@
+name: mingw
+
+on:
+  push:
+    paths:
+    - Dockerfile.mingw
+  schedule:
+  - cron: '30 1 * * *'
+
+permissions: read-all
+
+jobs:
+  build:
+    runs-on: ubuntu-22.04
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v3
+    - name: Build
+      uses: docker/build-push-action@v5
+      with:
+        file: Dockerfile.mingw
+        context: .