github/workflow: remove Cygwin build from Github Actions.

It often cross the 15 minutes timeout limit, so we just give up for now.

.github/workflows/build.yml

@@ -93,52 +93,6 @@ jobs:
       - name: Build and test
         run: rake -m test:build && rake test:run
 
-  Windows-Cygwin:
-    runs-on: windows-latest
-    timeout-minutes: 15
-    env:
-      ACTIONS_ALLOW_UNSECURE_COMMANDS: true
-      MRUBY_CONFIG: ci/gcc-clang
-      CC: gcc
-      installer-path: '%TMP%\cygwin-setup.exe'
-      cygwin-root: C:\cygwin
-      package-dir: C:\cygwin-package
-      cache-version: v1
-    steps:
-      - uses: actions/checkout@v3
-      - uses: actions/cache@v3
-        with:
-          path: ${{ env.package-dir }}
-          key: ${{ runner.os }}-cygwin-${{ env.cache-version }}
-      - name: Download Cygwin installer
-        shell: cmd
-        run: >
-          bitsadmin /transfer download /priority foreground
-          https://cygwin.com/setup-x86_64.exe ${{ env.installer-path }}
-      - name: Install Cygwin
-        shell: cmd
-        run: >
-          ${{ env.installer-path }}
-          --quiet-mode --no-shortcuts --no-startmenu --no-desktop --no-admin
-          --only-site --site http://mirrors.kernel.org/sourceware/cygwin/
-          --root ${{ env.cygwin-root }}
-          --local-package-dir ${{ env.package-dir }}
-          --packages gcc-core,gcc-g++,ruby
-      - name: Set PATH for Cygwin
-        run: |
-          echo '::set-env name=PATH::${{ env.cygwin-root }}\bin;${{ env.cygwin-root }}\usr\bin'
-      - name: Ruby version
-        shell: cmd
-        run: ruby -v
-      - name: Compiler version
-        run: ${{ env.CC }} --version
-      - name: Build and test
-        shell: cmd
-        run: ruby /usr/bin/rake -m test:build && ruby /usr/bin/rake test:run
-      - name: Set PATH for cache archiving (tar)
-        # set Windows path so that Cygwin tar is not used for cache archiving
-        run: echo '::set-env name=PATH::C:\windows\System32'
-
   Windows-VC:
     runs-on: windows-2022
     timeout-minutes: 10