fix(ci): run Lean image builds on dispatch

Author: morluto

.github/workflows/lean-images.yml

@@ -29,7 +29,7 @@ env:
 jobs:
   build-pr:
     name: Build ${{ matrix.image }}
-    if: github.event_name == 'pull_request'
+    if: github.event_name == 'pull_request' || github.event_name == 'workflow_dispatch'
     runs-on: ubuntu-latest
     timeout-minutes: 30
     strategy: