Bug 1556767 - Increase max-run-time for linux64 ccov jsreftest; r=egao

These tasks normally run in 45 to 55 minutes; if they exceed 60 minutes, the
task fails. Failures are not frequent, but I would like to avoid them. We could
increase chunks, but it looks like we have handled the other ccov cases like
this, by increasing the max-run-time.

Differential Revision: https://phabricator.services.mozilla.com/D33656

--HG--
extra : moz-landing-system : lando

taskcluster/ci/test/reftest.yml

@@ -93,6 +93,7 @@ jsreftest:
             android-em.*: 7200
             windows10-64-ccov/debug: 7200
             macosx.*64-ccov/debug: 7200
+            linux.*64-ccov/debug: 7200
             default: 3600
     tier:
         by-test-platform: