break out matrix startup into separate step

Author: habdelra

.github/workflows/ci.yaml

@@ -374,6 +374,9 @@ jobs:
         env:
           NODE_OPTIONS: --max_old_space_size=4096
         working-directory: packages/host
+      - name: Start matrix
+        run: pnpm start:matrix &
+        working-directory: packages/realm-server
       - name: Start realm servers
         run: PG_INDEXER=true pnpm start:all &
         working-directory: packages/realm-server