[KNI] ghactions: rotate stable branches

we want to cover most recent 3 stable branches;
so 4.18 enter the pool, and ancient 4.12 exits.

Signed-off-by: Francesco Romani <[email protected]>

Author: ffromani

.github/workflows/ci.yaml

@@ -2,9 +2,9 @@ name: CI Go
 
 on:
   push:
-    branches: [ master, release-4.12, release-4.14, release-4.16 ]
+    branches: [ master, release-4.14, release-4.16, release-4.18 ]
   pull_request:
-    branches: [ master, release-4.12, release-4.14, release-4.16 ]
+    branches: [ master, release-4.14, release-4.16, release-4.18 ]
 
 jobs:
   commit-check: