fix: consistent allowed_states guard in postgres.schema_pillar

Same `sls.split('.')[0]` pattern as ext_pillar_postgres + pg_notify_pillar_engine.
For sls='postgres.schema_pillar' the split happened to evaluate 'postgres',
which is in manager_states, so the guard worked accidentally — but it would
break silently if anyone ever moved the file under a deeper SLS path. Switch
to a literal `{% if 'postgres' in allowed_states %}` for the same intent-
revealing pattern as the master.d guards.

salt/postgres/schema_pillar.sls

@@ -4,7 +4,7 @@
 # Elastic License 2.0.
 
 {% from 'allowed_states.map.jinja' import allowed_states %}
-{% if sls.split('.')[0] in allowed_states %}
+{% if 'postgres' in allowed_states %}
 {%   from 'vars/globals.map.jinja' import GLOBALS %}
 
 # Deploys the so_pillar schema (tables, views, audit triggers, secrets,