ci: don't cancel on main (#27142)

.github/workflows/build.yml

@@ -26,7 +26,7 @@ permissions:
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.number || github.ref }}
-  cancel-in-progress: true
+  cancel-in-progress: ${{ github.ref_name != 'main' }}
 
 env:
   # Currently no way to detect automatically (#8153)