Merge pull request rails#51783 from JoeDupuis/fix-fail-fast-flake

Fix test runner --fail-fast test flake

Author: rafaelfranca

railties/test/application/test_runner_test.rb

@@ -782,8 +782,9 @@ def test_verify_fail_fast
             assert false
           end
 
-          10.times do |n|
+          4.times do |n|
             define_method("test_verify_fail_fast_\#{n}") do
+              sleep 0.1
               assert true
             end
           end