[build] Run `macos_legacy` job on `macos-12` (#9804)

`macos-latest` has been bumped to `macos-14-arm64` which breaks the builds

Authored by: bashonly

.github/workflows/build.yml

@@ -300,7 +300,7 @@ jobs:
   macos_legacy:
     needs: process
     if: inputs.macos_legacy
-    runs-on: macos-latest
+    runs-on: macos-12
 
     steps:
       - uses: actions/checkout@v4