Bug 1608251 - run reftest/reftest-no-accel on ubuntu1804 ccov and deactivate on linux64 r=marco,gbrown

Changes:

Enable reftest/reftest-no-accel on ubuntu1804/linux1018.
Remove reftest/reftest-no-accel from running on ubuntu1604/linux64.

Differential Revision: https://phabricator.services.mozilla.com/D59825

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

taskcluster/ci/test/test-sets.yml

@@ -30,8 +30,6 @@ common-tests:
     - mochitest-gpu
     - mochitest-media
     - mochitest-webgpu
-    - reftest
-    - reftest-no-accel
     - telemetry-tests-client
     - test-verify
     - test-verify-gpu
@@ -392,6 +390,8 @@ linux1804-ccov-tests:
     - mochitest-webgl1-ext
     - mochitest-webgl2-core
     - mochitest-webgl2-ext
+    - reftest
+    - reftest-no-accel
 
 linux-qr-tests:
     - mochitest