Add to branches_main

To keep non-latent master changes to a minium we plan for 4 more
11.x series releases.

This way non-latent workers will pick up jobs as these new branches
becomes active (every 3 months).

constants.py

@@ -14,6 +14,11 @@
         '11.1',
         '11.2',
         '11.3',
+        '11.4',
+        '11.5',
+        '11.6',
+        '11.7',
+        '11.8',
         ]
 
 # Defines what builders report status to GitHub