feat: add workflow_dispatch trigger for manual CI runs

feature/fix branches can now be triggered manually via workflow_dispatch;
release/main/maint branches retain both automatic and manual triggers.

Author: vistart

.github/workflows/test.yml

@@ -12,6 +12,7 @@ on:
       - main
       - 'release/v**'
       - 'maint/**'
+  workflow_dispatch:
 
 permissions:
   contents: read