[github] key the clang cache on the runner arch

Summary: This is to distinguish arm vs intel macs.

Differential Revision: D58826655

fbshipit-source-id: 9fcbc8db8cc0da4396aa59bf4ec62e4ad669766c

Author: jvillard

.github/workflows/install.yml

@@ -107,7 +107,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: facebook-clang-plugins/clang/install
-          key: clang-${{ runner.os }}-${{ steps.clang-hash.outputs.value }}
+          key: clang-${{ runner.os }}-${{ runner.arch }}-${{ steps.clang-hash.outputs.value }}
 
       - name: Record that the clang cache was hit
         if: steps.cache-clang.outputs.cache-hit == 'true'