test-docker-image.yml: Test Docker images also for all version bumbs

Let's do a Docker image build also on every new Rakudo-Star version, not only on `Dockerfile` changes.

Should hopefully discover issues BEFORE we even get into issues with the `official Docker image build`, see also
- docker-library/official-images#18923

Author: AntonOks

.github/workflows/test-docker-image.yml

@@ -5,13 +5,14 @@ on:
     branches: [ master ]
     paths:
     - '**/**/Dockerfile'
+    - 2[0-9]+.[0-1][0-1]'**'
   pull_request:
     branches: [ master ]
     paths:
     - '**/**/Dockerfile'
+    - 2[0-9]+.[0-1][0-1]'**'
 
 jobs:
-
   setup:
     runs-on: ubuntu-latest
     outputs: