Backport PR #1918: (fix): correct workflow branch selection (#1919)

Co-authored-by: Philipp A <flying-sheep@web.de>

Author: meeseeksmachine

.github/workflows/test-cpu.yml

@@ -4,7 +4,7 @@ on:
   push:
     branches:
       - main
-      - "*.*.x"
+      - "[0-9]+.[0-9]+.x"
   pull_request:
 
 env: