test: Increase test coverage on auditable resources (#7038)

* test: Increase test coverage on auditable resources

When adding a new audit resource, we also need to add it to the
function switch statements. This is a likely mistake, now a unit
test will check this for you

coderd/database/migrations/000115_workspace_proxy_resource.down.sql

@@ -0,0 +1,2 @@
+-- It's not possible to drop enum values from enum types, so the UP has "IF NOT
+-- EXISTS".

coderd/database/migrations/000115_workspace_proxy_resource.up.sql

@@ -0,0 +1 @@
+ALTER TYPE resource_type ADD VALUE IF NOT EXISTS 'workspace_proxy';