Bug 1430668 - Increase chunks for linux32/debug jsreftest; r=me, a=test-only

Attempt to avoid intermittent task timeouts in these tests.

taskcluster/ci/test/reftest.yml

@@ -64,6 +64,7 @@ jsreftest:
             windows10-64-ccov/debug: 5
             linux64-ccov/.*: 5
             linux64-qr/.*: 4
+            linux32/debug: 5
             macosx.*: 2
             default: 3
     e10s: