GitHub Actions: Remove macos-latest from libraries-test-suite.

It doesn't work and needs fixing elsewhere before it can be
enabled again. (Perhaps the macOS download is missing libgc.)

Author: waywardmonkeys

.github/workflows/libraries-test-suite.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [macos-latest, ubuntu-latest]
+        os: [ubuntu-latest]
     steps:
       - uses: actions/checkout@v3
         with: