Add Rocky Linux to GitHub actions

Signed-off-by: Enrico Usai <[email protected]>

Author: enrico-usai

.github/workflows/dokken-system-tests.yml

@@ -34,6 +34,7 @@ jobs:
           - ubuntu2004
           - ubuntu2204
           - rhel8
+          - rocky8
       fail-fast: false
     steps:
       - uses: actions/checkout@main