Skip test_via_to_sql_with_complicating_connection for PostgreSQL 19+

PostgreSQL 19 no longer allows setting standard_conforming_strings to OFF.

```sql
postgres=# SET standard_conforming_strings = off;
ERROR:  non-standard string literals are not supported
postgres=# select version();
                           version
--------------------------------------------------------------------
 PostgreSQL 19devel on x86_64-linux, compiled by gcc-15.2.1, 64-bit
(1 row)
```

According to rails#14632, the purpose of the failing test is to ensure that the unescape_bytea method is per-connection, not global.
Since PostgreSQL 19dev no longer allows setting standard_conforming_strings to OFF, the value will no longer vary per connection,
so  we can skip this test when the PostgreSQL version is 19 or higher.

Fix rails#56789

Author: yahonda

activerecord/test/cases/adapters/postgresql/bytea_test.rb

@@ -110,6 +110,8 @@ def test_via_to_sql
   end
 
   def test_via_to_sql_with_complicating_connection
+    skip "PostgreSQL 19+ no longer allows setting standard_conforming_strings to OFF" if @connection.database_version >= 190000
+
     Thread.new do
       other_conn = ActiveRecord::Base.lease_connection
       other_conn.execute("SET standard_conforming_strings = off")