[test] Speed up unicode-regexp-zero-length_test.

After 347b72c260949fa96ec5a45f3d6b1e2388ea245a, this test began timing out on dartk-mac-debug-simdbc64.

Change-Id: I84fc6457c7e10068f761d25cbb1241e2c2f8ab49
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/100902
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>
diff --git a/tests/corelib_2/regexp/unicode-regexp-zero-length_test.dart b/tests/corelib_2/regexp/unicode-regexp-zero-length_test.dart
index 1d07628..e1dd330 100644
--- a/tests/corelib_2/regexp/unicode-regexp-zero-length_test.dart
+++ b/tests/corelib_2/regexp/unicode-regexp-zero-length_test.dart
@@ -72,7 +72,7 @@
   }
 
   // Test with a lot of copies.
-  const c = 1000;
+  const c = 100;
   ms = u.allMatches((L + T) * c);
   assertEquals(c + 1, ms.length);
   for (var i = 0; i < ms.length; i++) {