Bug 1565949 - Bump the runtime of mingwclang x86 debug reftests r=firefox-build-system-reviewers,mshal

Differential Revision: https://phabricator.services.mozilla.com/D38026

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

taskcluster/ci/test/reftest.yml

@@ -137,6 +137,7 @@ reftest:
     max-run-time:
         by-test-platform:
             android-em.*: 7200
+            windows7-32-mingwclang/debug: 5400
             windows10-64-ccov/debug: 5400
             windows10-64-asan/opt: 5400
             macosx.*64-ccov/debug: 5400