Revert "ci: Build mingw image"

This reverts commit a02ceeb646.

.github/workflows/mingw.yml

@@ -1,24 +0,0 @@
-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: .