Allow manual trigger of the Build action

Signed-off-by: Nikolay Blagoev <[email protected]>

Author: nblagoev

.github/workflows/build.yml

@@ -8,6 +8,7 @@ on:
   pull_request:
     branches:
       - master
+  workflow_dispatch: {}
 jobs:
   cleanup-runs: # automatically cancel CI runs on pushes to the same branch
     runs-on: ubuntu-latest