gha: add docker engine v28.x to the test-matrix

currently v28.0.0-rc.1

Signed-off-by: Sebastiaan van Stijn <[email protected]>

.github/workflows/ci.yml

@@ -156,6 +156,7 @@ jobs:
         engine:
           - 26
           - 27
+          - 28
     steps:
       - name: Prepare
         run: |