Install MinGW from GitHub NuGet registry

Attempt to workaround recent, frequent failures of the MinGW jobs by
installing an internalized Chocolatey package hosted on GitHub.

.github/workflows/windows.yml

@@ -18,10 +18,31 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
-      - name: Set up MinGW
-        uses: egor-tensin/setup-mingw@v2
-        with:
-          platform: ${{ matrix.architecture }}
+      - name: Download MinGW 8.1.0
+        run: |
+          $headers = @{Authorization = 'Bearer ${{ secrets.GITHUB_TOKEN }}'}
+          $uri = 'https://nuget.pkg.github.com/falbrechtskirchinger/download/mingw/8.1.0/mingw.8.1.0.nupkg'
+          Invoke-WebRequest -Uri $uri -Headers $headers -OutFile mingw.8.1.0.nupkg
+      - name: Uninstall MinGW
+        continue-on-error: true
+        run: choco uninstall mingw
+      # Based on egor-tensin/setup-mingw
+      - name: Install MinGW 8.1.0
+        run: |
+          choco install mingw.8.1.0.nupkg ${{ matrix.architecture == 'x86' && '--x86' || '' }}
+          $prefix = "${{ matrix.architecture == 'x64' && 'x86_64-w64-mingw32' || 'i686-w64-mingw32' }}"
+          $mingw = "${{ matrix.architecture == 'x64' && 'mingw64' || 'mingw32' }}"
+          $mingw_install = Join-Path C: ProgramData chocolatey lib mingw tools install
+          $mingw_root = Join-Path $mingw_install $mingw
+          $mingw_bin = Join-Path $mingw_root bin
+          $mingw_lib = Join-Path $mingw_root $prefix lib
+          echo $mingw_bin >> $env:GITHUB_PATH
+          Remove-Item (Join-Path $mingw_lib 'libpthread.dll.a')
+          Remove-Item (Join-Path $mingw_lib 'libwinpthread.dll.a')
+      #- name: Set up MinGW
+      #  uses: egor-tensin/setup-mingw@v2
+      #  with:
+      #    platform: ${{ matrix.architecture }}
       - name: cmake
         run: cmake -S . -B build -G "MinGW Makefiles" -DCMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On
       - name: build