changed self-hosted (#7212)

Signed-off-by: Sally MacFarlane <[email protected]>

Author: macfarla

.github/workflows/docker.yml

@@ -34,7 +34,7 @@ jobs:
       matrix:
         platform:
           - ubuntu-22.04
-          - [self-hosted, ARM64]
+          - besu-arm64
     runs-on: ${{ matrix.platform }}
     steps:
       - name: Prepare