chore(CI): Split basepath test suite into smaller and more parallel test suites

Author: bgw

.github/workflows/build_and_test.yml

@@ -801,7 +801,8 @@ jobs:
 
         NEXT_TEST_MODE=start BROWSER_NAME=safari node run-tests.js \
           test/production/pages-dir/production/test/index.test.ts \
-          test/e2e/basepath/basepath.test.ts
+          test/e2e/basepath/basepath.test.ts \
+          test/e2e/basepath/error-pages.test.ts
 
         BROWSER_NAME=safari DEVICE_NAME='iPhone XR' node run-tests.js \
           test/production/prerender-prefetch/index.test.ts