PG17 compatibility: fix pg16 to pg17 upgrade (#7788)

In `citus_prepare_upgrade()`, don't drop any_value when upgrading from
PG16+, because PG16+ has its own any_value function. Attempting to do so
results in the error seen in [pg16-pg17
upgrade](https://github.com/citusdata/citus/actions/runs/11768444117/job/32778340003?pr=7661):
```
ERROR:  cannot drop function any_value(anyelement) because it is required by the database system
CONTEXT:  SQL statement "DROP AGGREGATE IF EXISTS pg_catalog.any_value(anyelement)"
```
When 16 becomes the minimum supported Postgres version, the drop
statements can be removed.

src/backend/distributed/sql/citus--12.1-1--13.0-1.sql

@@ -1,3 +1,4 @@
 -- citus--12.1-1--13.0-1.sql
 
 -- bump version to 13.0-1
+#include "udfs/citus_prepare_pg_upgrade/13.0-1.sql"

src/backend/distributed/sql/udfs/citus_prepare_pg_upgrade/latest.sql

@@ -18,13 +18,15 @@ BEGIN
     DROP AGGREGATE IF EXISTS array_cat_agg(anyarray);
     DROP AGGREGATE IF EXISTS array_cat_agg(anycompatiblearray);
 
-    -- We should drop any_value because PG16 has its own any_value function
+    -- We should drop any_value because PG16+ has its own any_value function
     -- We can remove this part when we drop support for PG16
-    DELETE FROM pg_depend WHERE
-        objid IN (SELECT oid FROM pg_proc WHERE proname = 'any_value' OR proname = 'any_value_agg') AND
-        refobjid IN (select oid from pg_extension where extname = 'citus');
-    DROP AGGREGATE IF EXISTS pg_catalog.any_value(anyelement);
-    DROP FUNCTION IF EXISTS pg_catalog.any_value_agg(anyelement, anyelement);
+    IF substring(current_Setting('server_version'), '\d+')::int < 16 THEN
+        DELETE FROM pg_depend WHERE
+            objid IN (SELECT oid FROM pg_proc WHERE proname = 'any_value' OR proname = 'any_value_agg') AND
+            refobjid IN (select oid from pg_extension where extname = 'citus');
+        DROP AGGREGATE IF EXISTS pg_catalog.any_value(anyelement);
+        DROP FUNCTION IF EXISTS pg_catalog.any_value_agg(anyelement, anyelement);
+    END IF;
 
     --
     -- Drop existing backup tables