manual-test: install MSYS2 on Windows/ARM64

The Windows/ARM64 runners that are currently in public preview do not
have MSYS2 installed by default, so let's do that.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/manual-test.yml

@@ -45,6 +45,18 @@ jobs:
     if: ${{ inputs.container-runs-on == '(none)' }}
     runs-on: ${{ inputs.runs-on }}
     steps:
+      - uses: msys2/setup-msys2@v2
+        # The public preview of GitHub-hosted Windows/ARM64 runners lacks
+        # a working MSYS2 installation, so we need to set it up ourselves.
+        if: ${{ inputs.runs-on == 'windows-11-arm' }}
+        with:
+          msystem: 'CLANGARM64'
+          # We cannot use `C:\` because `msys2/setup-msys2` erroneously
+          # believes that an MSYS2 exists at `C:\msys64`, but it doesn't,
+          # which is the entire reason why we need to set it up in this
+          # here step... However, by using `C:\.\` we can fool that
+          # overzealous check.
+          location: C:\.\
       - uses: actions/checkout@v4
       - uses: ./
         with: