Fix publish script

Summary:
Changelog: Fix js-flipper package being published empty

Build js-flipper before publishing

Fixes(?) https://github.com/facebook/flipper/issues/3023

Reviewed By: jknoxville

Differential Revision: D32201978

fbshipit-source-id: 962b14fe1b5accb99bb06c098d86a6824599c967

.github/workflows/publish-npm.yml

@@ -29,5 +29,8 @@ jobs:
         run: yarn publish
         working-directory: react-native/react-native-flipper
       - name: Publish JS Flipper
-        run: yarn publish
         working-directory: js/js-flipper
+        run: |
+          yarn
+          yarn build
+          yarn publish