Fix macOS Python 3.11 build by removing brewed liblzma

Python 3.11 is now the first actions/setup-python Python built
to target universal2 (i.e., x86_64/arm64 multiarch) on macOS.

Brewed packages such as xz (which provides liblzma.dylib and liblzma.a)
are built for only a single native architecture. This led to build and
configure failures when the native-only liblzma.dylib was linked against
by a multiarch compilation.

Work around this by unlinking the xz package so that this brewed library
is not found by the linker, failing back to the system .tbd file instead.
If later build steps use brewed commands that need this library, we may
need to `brew link` it again later, but for now we get away without it.

Author: jmarshall

.github/workflows/ci.yaml

@@ -10,15 +10,13 @@ jobs:
         os: [ubuntu, macos]
         python-version: ['3.7', '3.8', '3.9', '3.10', '3.11']
         exclude:
-          # Run only the latest 3.x on macOS
+          # Run only the latest two 3.x versions on macOS
           - os: macos
             python-version: 3.7
           - os: macos
             python-version: 3.8
           - os: macos
             python-version: 3.9
-          - os: macos
-            python-version: 3.11
 
     steps:
       - name: Checkout pysam
@@ -32,12 +30,18 @@ jobs:
       - name: Install prerequisite Python libraries
         run:  pip install cython pytest pytest-pep8
 
-      - name: Install build prerequisites
+      - name: Install Linux build prerequisites
         if:   runner.os == 'Linux'
         run: |
           sudo apt-get update
           sudo apt-get install -q --no-install-recommends --no-install-suggests libcurl4-openssl-dev
 
+      - name: Update macOS build prerequisites
+        if:   runner.os == 'macOS'
+        run: |
+          # Remove brewed liblzma (if any), as it is not multiarch
+          brew unlink xz || true
+
       - name: Build (directly from checkout)
         run:  python setup.py build