make the shell configurable (default to bash)

action.yml

@@ -8,11 +8,28 @@ inputs:
   working-directory:
     description: "working directory"
     required: false
+  shell:
+    description: "shell (options: 'bash' or 'msys2 {0}')"
+    default: "bash"
+    required: false
 
 runs:
   using: "composite"
   steps:
-    - shell: bash
+    - name: create bash-or-msys2
+      shell: bash
+      run: |
+        if [[ "${{ inputs.shell }}" == "msys2 {0}" ]]; then
+          if [[ ! -f "D:/a/_temp/setup-msys2/bash-or-msys2.cmd" ]]; then
+            powershell New-Item -ItemType SymbolicLink -Path "D:/a/_temp/setup-msys2/bash-or-msys2.cmd" -Target "D:/a/_temp/setup-msys2/msys2.cmd"
+          fi
+        elif [[ "${{ inputs.shell }}" == "bash" ]]; then
+          sudo ln -sf $(which bash) /usr/local/bin/bash-or-msys2
+        else
+          echo "unknown shell: ${{ inputs.shell }}"
+          exit 1
+        fi
+    - shell: bash-or-msys2 {0}
       working-directory: ${{ inputs.working-directory }}
       run: |
         status=0