Run recursive yarn install for deps

`yarn install` only gets deps for the top level package.json, custom
script `yarn setup` will get deps for all three nested package.json
folders (/, /polygerrit-ui, /polygerrit-ui/app)

Change-Id: I507bdbfea617f401b766f15d3a0ab2e676471cac
diff --git a/recipes/recipes/gerrit-web-tests.py b/recipes/recipes/gerrit-web-tests.py
index 0d8a94c..8e80a6d 100644
--- a/recipes/recipes/gerrit-web-tests.py
+++ b/recipes/recipes/gerrit-web-tests.py
@@ -64,7 +64,7 @@
     with api.nodejs(version='18.11.0'):
       # Named steps to test the change
       api.step('install yarn', ['npm', 'install', '-g', 'yarn'])
-      api.step('install deps', ['yarn', 'install'])
+      api.step('install deps', ['yarn', 'setup'])
       api.step('run tests', ['yarn', 'test'])