test: run e2e tests in WebKit on macOS (#40140)

WebKit was removed from the e2e tests in
https://github.com/go-gitea/gitea/pull/37315 because Linux WebKit kept
crashing. `make test-e2e` on macOS now also runs WebKit, which does not
show these crashes there. CI stays on Linux, because macOS runners would
need about an extra GB of cache storage.

1. The bot account test clicks the user type dropdown, Safari only moves
Tab focus between text fields
1. On macOS, Playwright runs with a single libuv thread, concurrent
`getaddrinfo` lookups of `localhost` there sporadically stall for 5s

---------

Signed-off-by: silverwind <me@silverwind.io>

tools/test-e2e.sh

@@ -190,6 +190,11 @@ export GITEA_TEST_E2E_PASSWORD
 export GITEA_TEST_E2E_EMAIL
 export GITEA_TEST_E2E_TIMEOUT_FACTOR
 
+# concurrent localhost lookups on macOS sporadically stall for 5s
+if [ "$(uname -s)" = "Darwin" ]; then
+  export UV_THREADPOOL_SIZE=1
+fi
+
 if [ "$PLAYWRIGHT_MODE" = "container" ]; then
   export PW_TEST_CONNECT_WS_ENDPOINT="ws://127.0.0.1:${PLAYWRIGHT_SERVER_PORT}/"
 fi