message: CI: actually run the msys2 shell!
diff: @@ -10,14 +10,19 @@ jobs:
  - name: Linux
  os: ubuntu-latest
  artifact: build-Linux release
  + shell: bash {0}
  - name: macOS
  os: macos-latest
  artifact: build-macOS
  + shell: bash -euxo pipefail {0}
  - name: Windows
  os: windows-latest
  shell: msys2 {0}
  artifact: build-Windows
  runs-on: ${{ matrix.os }}
  + defaults:
  + run:
  + shell: ${{ matrix.shell }}
  name: ${{ matrix.name }}
  steps:
  - name: Checkout
  