fix: Fix 500 error on issues view

The pgpubsub trigger for caching issues wasn't imported and thus didn't
run in the past.

Author: Erethon

src/shared/listeners/__init__.py

@@ -2,3 +2,4 @@
 import shared.listeners.nix_evaluation  # noqa
 import shared.listeners.automatic_linkage  # noqa
 import shared.listeners.cache_suggestions  # noqa
+import shared.listeners.cache_issues  # noqa