Add Xcode 14 to GitHub Actions

This changelist adds an Xcode 14 configuration to the build matrix in GitHub Actions.

Author: jstone-lucasfilm

.github/workflows/main.yml

@@ -70,16 +70,16 @@ jobs:
           cmake_config: -DMATERIALX_BUILD_SHARED_LIBS=ON
           python: 3.7
 
-        - name: MacOS_Xcode_12_Python37
-          os: macos-11
+        - name: MacOS_Xcode_13_Python39
+          os: macos-12
           compiler: xcode
-          compiler_version: "12.4"
-          python: 3.7
+          compiler_version: "13.4"
+          python: 3.9
 
-        - name: MacOS_Xcode_13_Python39
+        - name: MacOS_Xcode_14_Python39
           os: macos-12
           compiler: xcode
-          compiler_version: "13.3"
+          compiler_version: "14.2"
           python: 3.9
           test_shaders: ON