Keep Go 1.21 macOS tests on a compatible runner

Use the supported macos-15 image for the macOS leg while retaining its existing check name. macOS 26 dyld rejects Go 1.21.3 internal-linker binaries without LC_UUID; preserve the established Go toolchain instead of bumping it. Keep Linux/Windows runners, all SHA pins, build steps, race tests, timeouts, and matrix coverage unchanged.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: mrecachinas

.github/workflows/test.yml

@@ -9,7 +9,8 @@ jobs:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
       fail-fast: false
-    runs-on: ${{ matrix.os }}
+    # Preserve Go 1.21 coverage: macOS 26 rejects its linker output without LC_UUID.
+    runs-on: ${{ matrix.os == 'macos-latest' && 'macos-15' || matrix.os }}
     steps:
       - name: Set up Go
         uses: actions/setup-go@924ae3a1cded613372ab5595356fb5720e22ba16 # v6.5.0