Bug 1584692 - Increase max-run-time for win7 xpcshell opt; r=bc

Avoid intermittent task timeouts.

Differential Revision: https://phabricator.services.mozilla.com/D48131

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

taskcluster/ci/test/xpcshell.yml

@@ -60,7 +60,7 @@ xpcshell:
         by-test-platform:
             macosx.*(?!-ccov)...../.*: 3600
             windows10-aarch64/.*: 3600
-            windows7-32(-shippable)?/opt: 3600
+            windows7-32(-shippable)?/opt: 5400
             .*-ccov/debug: 5400
             default: 2700
     allow-software-gl-layers: false