Small fix.

Author: oleburghardt

.github/workflows/regression.yml

@@ -229,7 +229,7 @@ jobs:
       include:
         - testscript: 'serial_regression_AD.py'
           #tag: TagNoMP, check:
-          tag:NoMPI
+          tag: NoMPI
     steps:
       - name: Pre Cleanup
         uses: docker://ghcr.io/su2code/su2/test-su2:240320-1536