refactor github actions

Author: sebsto

.github/workflows/build_soundness.yml

@@ -3,6 +3,15 @@ name: Build, tests & soundness checks
 on: [push, pull_request]
 
 jobs:
+  swift-bedrock-library:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Run tests
+        working-directory: swift-bedrock-library
+        run: swift test
+
   playground-backend:
     runs-on: ubuntu-latest
     steps: