[build] Enable swarming on fuzzer builder

This prepares for:
https://chromium-review.googlesource.com/c/chromium/tools/build/+/743381

NOTRY=true

Bug: v8:7012
Change-Id: Ic40aa08cbc7b68b2a1b55924536a319f729a557a
Reviewed-on: https://chromium-review.googlesource.com/743363Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49030}

infra/mb/mb_config.pyl

@@ -412,7 +412,7 @@
     'gn_release_x64_concurrent_marking': [
       'gn', 'release_bot', 'x64', 'v8_enable_concurrent_marking', 'swarming'],
     'gn_release_x64_correctness_fuzzer' : [
-      'gn', 'release_bot', 'x64', 'v8_correctness_fuzzer'],
+      'gn', 'release_bot', 'x64', 'v8_correctness_fuzzer', 'swarming'],
     'gn_release_x64_fuchsia': [
       'gn', 'release_bot', 'x64', 'fuchsia', 'swarming'],
     'gn_release_x64_fuchsia_trybot': [