fix fatimage concurrency

Author: sjpb

.github/workflows/fatimage.yml

@@ -15,7 +15,7 @@ jobs:
   openstack:
     name: openstack-imagebuild
     concurrency:
-      group: ${{ github.workflow }}-${{ github.ref }}-${{ matrix.os_version }}-${{ matrix.build }} # to branch/PR + OS + build
+      group: ${{ github.workflow }}-${{ github.ref }}-${{ matrix.builds.label }}
       cancel-in-progress: true
     runs-on: ubuntu-22.04
     strategy: