chore(CI): Split basepath test suite into smaller and more parallel test suites (#78892)

Same basic idea as #78787

This test suite has a lot of timeouts with rspack, which causes it to take a long time to run (though not quite long enough that it breaks the job).

In general, large test suites are good to break up, because they benefit from parallelism.

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