test(aws-lambda): run npm ci when building packages

Author: yousif-bugsnag

test/aws-lambda/features/scripts/build-fixtures

@@ -45,6 +45,7 @@ end
 # Build Bugsnag packages so they're ready to install
 def build
   Dir.chdir(ROOT) do
+    system("npm ci")
     system("npm run build")
   end
 end