Use macOS 11 for older toolchains

Signed-off-by: Yuki Okushi <jtitor@2k36.org>

Author: JohnTitor

.github/workflows/bors.yml

@@ -259,32 +259,32 @@ jobs:
 
     name: Build Channels macOS
     needs: macos
-    runs-on: macos-12
     env:
       OS: macos
     strategy:
       fail-fast: true
       max-parallel: 4
       matrix:
-        toolchain: [
-          stable,
-          beta,
-          nightly,
-          1.13.0,
-          1.19.0,
-          1.24.0,
-          1.25.0,
-          1.30.0,
-        ]
+        target:
+          - { toolchain: stable, os: macos-12 }
+          - { toolchain: beta, os: macos-12 }
+          - { toolchain: nightly, os: macos-12 }
+          # Use macOS 11 for older toolchains as newer Xcode donesn't work well.
+          - { toolchain: 1.13.0, os: macos-11 }
+          - { toolchain: 1.19.0, os: macos-11 }
+          - { toolchain: 1.24.0, os: macos-11 }
+          - { toolchain: 1.25.0, os: macos-11 }
+          - { toolchain: 1.30.0, os: macos-11 }
+    runs-on: ${{ matrix.target.os }}
     steps:
       - uses: rust-lang/simpleinfra/github-actions/cancel-outdated-builds@master
         with:
           github_token: "${{ secrets.GITHUB_TOKEN }}"
       - uses: actions/checkout@v3
       - name: Setup Rust toolchain
-        run: TOOLCHAIN=${{ matrix.toolchain }} sh ./ci/install-rust.sh
+        run: TOOLCHAIN=${{ matrix.target.toolchain }} sh ./ci/install-rust.sh
       - name: Execute build.sh
-        run: LIBC_CI=1 TOOLCHAIN=${{ matrix.toolchain }} sh ./ci/build.sh
+        run: LIBC_CI=1 TOOLCHAIN=${{ matrix.target.toolchain }} sh ./ci/build.sh
 
   build_channels_windows:
     permissions: