[CI] Updating to macOS 12 due to deprecation of 10.15.

I originally had things on 10.15 since it matched what my old MacBook was officially capable of, but it is being deprecated:
actions/runner-images#5583
Since we only support macOS for CI purposes as an early warning of compatibility issues, I don't think it's worth chasing old versions so I'm skipping over macOS 11.

Author: PathogenDavid

.github/workflows/ClangSharp.Pathogen.yml

@@ -46,8 +46,8 @@ jobs:
             libclang-subpath: lib/libclang.so
             build-command: ./build-native.sh
             skip-python-install: true
-          - os: macos-10.15
-            name: MacOS x64
+          - os: macos-12
+            name: macOS x64
             rid: osx-x64
             libclang-subpath: lib/libclang.dylib
             build-command: ./build-native.sh

.github/workflows/keep-cache-warm.yml

@@ -43,8 +43,8 @@ jobs:
             libclang-subpath: lib/libclang.so
             build-command: ./build-native.sh
             skip-python-install: true
-          - os: macos-10.15
-            name: MacOS x64
+          - os: macos-12
+            name: macOS x64
             rid: osx-x64
             libclang-subpath: lib/libclang.dylib
             build-command: ./build-native.sh