Add workflow dispatch plus repo condition to scala-steward.yml

.github/workflows/scala-steward.yml

@@ -1,4 +1,5 @@
 on:
+  workflow_dispatch:
   schedule:
     - cron: '0 0 * * 0'
 
@@ -8,6 +9,7 @@ jobs:
   scala-steward:
     runs-on: ubuntu-22.04
     name: Launch Scala Steward
+    if: github.repository == 'apache/pekko-http'
     steps:
       - name: Launch Scala Steward
         uses: scala-steward-org/scala-steward-action@v2