[test] Add d8_default isolate to fuzzer bundle

TBR=sergiyb@chromium.org
NOTRY=true

Bug: v8:6972
Change-Id: Id1bdaa1fe4cd0a02f1b59eb7b7f4cecda36ded9a
Reviewed-on: https://chromium-review.googlesource.com/876004Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50713}

BUILD.gn

@@ -2824,6 +2824,7 @@ group("v8_clusterfuzz") {
 
   if (v8_test_isolation_mode != "noop") {
     deps += [
+      "test:d8_default_run",
       "tools:run-deopt-fuzzer_run",
       "tools:run-num-fuzzer_run",
     ]