shuffle tests in web_long_running_tests shard (#82394)

diff --git a/dev/bots/test.dart b/dev/bots/test.dart
index 47b7eaa..c81bfa3 100644
--- a/dev/bots/test.dart
+++ b/dev/bots/test.dart
@@ -864,6 +864,11 @@
       '--sound-null-safety',
     ]),
   ];
+
+  // Shuffling mixes fast tests with slow tests so shards take roughly the same
+  // amount of time to run.
+  tests.shuffle(math.Random(0));
+
   await _ensureChromeDriverIsRunning();
   await _runShardRunnerIndexOfTotalSubshard(tests);
   await _stopChromeDriver();