ci: add workflow_dispatch and concurrency group to fossa.yaml (#211)

fossa.yaml was missing both mandatory CI hygiene rules:
- workflow_dispatch for manual re-triggering of license scans
- concurrency group to prevent duplicate runs on rapid pushes

Signed-off-by: Sebastien Tardif <sebtardif@ncf.ca>

Author: SebTardif

.github/workflows/fossa.yaml

@@ -6,10 +6,15 @@ on:
   pull_request:
     branches: [main]
   merge_group: {}
+  workflow_dispatch: {}
 
 permissions:
   contents: read
 
+concurrency:
+  group: fossa-${{ github.ref }}
+  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
+
 env:
   FOSSA_CLI_VERSION: "3.17.10"