fix: reduce max parallel jobs in Docker publish workflow

Author: pablodz

.github/workflows/docker-publish.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
-      max-parallel: 4
+      max-parallel: 2
       matrix:
         asterisk_version: [ master, 23, 22, 21 ]
         base_version: [ 9-minimal ]