Bug 1692068 - Increase crashtest chunking on TSan r=decoder

TSan is prone to issues with slowdown and resource exhaustion. Increasing crashtest chunking appears to reduce the rate of restarts and intermittents related to timeouts.

Differential Revision: https://phabricator.services.mozilla.com/D110372

taskcluster/ci/test/reftest.yml

@@ -54,6 +54,7 @@ crashtest:
     chunks:
         by-test-platform:
             android-em-7.*: 1
+            linux.*64-tsan/opt: 8
             default: 1
     e10s: true
     run-on-projects: