Run blink_web_tests on fuchsia with one worker

Blink_web_tests on fuchsia now stuck in 'fork' startup method. We can
not switch to 'spawn' method due to a pickle issue which is fuchsia only.

This is a workaround to run blink_web_tests with only one worker, so
that we don't need to fork a child process to run the tests, thus fix
the timeout issue.

Bug: 1267498
Change-Id: I19af09fbaf1c90289fb2e1c0a5b600dc77b876b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3366742
Reviewed-by: Preethi Mohan <[email protected]>
Auto-Submit: Weizhong Xia <[email protected]>
Reviewed-by: Brian Sheedy <[email protected]>
Commit-Queue: Brian Sheedy <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Commit-Queue: Dirk Pranke <[email protected]>
Cr-Commit-Position: refs/heads/main@{#955376}
diff --git a/testing/buildbot/test_suite_exceptions.pyl b/testing/buildbot/test_suite_exceptions.pyl
index 98b75c0..c2bb18a 100644
--- a/testing/buildbot/test_suite_exceptions.pyl
+++ b/testing/buildbot/test_suite_exceptions.pyl
@@ -227,6 +227,7 @@
       'Fuchsia x64': {
         'args': [
           '--platform=fuchsia',
+          '--jobs=1',
         ],
         'swarming': {
           'shards': 1,