ci: Don't re-archive the tar.xz benchmark baseline

The new version of `actions/upload-artifact` allows for skipping the
automatic file zipping, which is good because our files are already
compressed.

library/compiler-builtins/.github/workflows/main.yaml

@@ -320,6 +320,7 @@ jobs:
       with:
         name: ${{ env.BASELINE_NAME }}
         path: ${{ env.BASELINE_NAME }}.tar.xz
+        archive: false # already compressed
 
     - name: Print test logs if available
       if: always()