Change test timeout from 5min to 15min

We have seen several times the CI hits this 5min limit

https://bazel.build/reference/test-encyclopedia#role-test-runner

Release-Notes: skip
Change-Id: I80abb35d96266a52ce928692e4eb3bc81622874c
diff --git a/polygerrit-ui/BUILD b/polygerrit-ui/BUILD
index 2f405e6..049f1d3 100644
--- a/polygerrit-ui/BUILD
+++ b/polygerrit-ui/BUILD
@@ -30,6 +30,7 @@
 
 nodejs_test(
     name = "web-test-runner",
+    size = "large",
     chdir = package_name(),
     data = [
         ":web-test-runner_config-sources",