[test] Skip es6/classes in stress mode on PPC

es6/classes is slow to run in stress mode and times out on PPC.
As a long term fix we should split this into multiple tests so
each individual test runs faster.

Bug: v8:9246
Change-Id: I95eed06d85f73cc66229dfbd83ac7521dcbbb54f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1615252
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Sergiy Belozorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61619}

test/mjsunit/mjsunit.status

@@ -915,7 +915,8 @@
 
   # Too slow for TSAN in stress mode.
   # Goes OOM on ODROID devices: https://crbug.com/v8/9026
-  'es6/classes': [PASS, SLOW, ['tsan or (arch == arm and not simulator_run)', SKIP]],
+  # Too slow on PPC: https://crbug.com/v8/9246
+  'es6/classes': [PASS, SLOW, ['tsan or (arch == arm and not simulator_run) or arch == ppc', SKIP]],
   'regress/regress-1122': [PASS, ['tsan', SKIP]],
 
   # Too slow with gc_stress on arm64.