btrfs-progs: ci: extend pattern for branches picked by devel workflow

Add a possibility to test branches independent of devel, the pattern is
prefix "ci/" or "CI/".

[ci skip]

Signed-off-by: David Sterba <dsterba@suse.com>

.github/workflows/devel.yml

@@ -8,6 +8,8 @@ on:
   push:
     branches:
       - devel
+      - 'ci/**'
+      - 'CI/**'
 jobs:
   build-simple:
     name: Simple build tests