Switch to macOS 12 since macos-11 is no longer available

Author: eregon

.github/workflows/build.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-20.04, ubuntu-22.04, ubuntu-24.04, macos-11, macos-arm-oss ]
+        os: [ ubuntu-20.04, ubuntu-22.04, ubuntu-24.04, macos-12, macos-arm-oss ]
         ruby: [jruby-9.3.15.0]
     runs-on: ${{ matrix.os }}
     steps:
@@ -24,7 +24,7 @@ jobs:
       id: platform
       run: |
         platform=${{ matrix.os }}
-        platform=${platform/macos-11/macos-latest}
+        platform=${platform/macos-12/macos-latest}
         platform=${platform/macos-arm-oss/macos-13-arm64}
         echo "platform=$platform" >> $GITHUB_OUTPUT
     - name: Set ruby