[dart/fuzzer] added another ignored parameter

Rationale:
Avoids rejecting extra parameter when running
on cluster for nightly testing.
Change-Id: I34a5e02638ec93f602609e32f5e460e774656f35
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/105968
Reviewed-by: Alexander Thomas <[email protected]>
Commit-Queue: Aart Bik <[email protected]>

Author: aartbik

runtime/tools/dartfuzz/dartfuzz_test.dart

@@ -586,6 +586,8 @@ main(List<String> arguments) {
         help: 'number of shards used in cluster run', defaultsTo: '1')
     ..addOption('shard', help: 'shard id in cluster run', defaultsTo: '1')
     ..addOption('output_directory',
+        help: 'path to output (ignored)', defaultsTo: null)
+    ..addOption('output-directory',
         help: 'path to output (ignored)', defaultsTo: null);
 
   // Starts fuzz testing session.