Address test_disable_extension_with_schema failure

This commit addresses the following failure.

```
$ ARCONN=postgresql bin/test test/cases/adapters/postgresql/extension_migration_test.rb test/cases/adapters/postgresql/postgresql_adapter_test.rb -n "/^(?:PostgresqlExtensionMigrationTest#(?:test_disable_extension_raises_when_dependent_objects_exist)|ActiveRecord::ConnectionAdapters::PostgreSQLAdapterTest#(?:test_disable_extension_with_schema))$/" --seed 3841 -v
Using postgresql
Run options: -n "/^(?:PostgresqlExtensionMigrationTest#(?:test_disable_extension_raises_when_dependent_objects_exist)|ActiveRecord::ConnectionAdapters::PostgreSQLAdapterTest#(?:test_disable_extension_with_schema))$/" --seed 3841 -v

PostgresqlExtensionMigrationTest#test_disable_extension_raises_when_dependent_objects_exist = 0.05 s = .
ActiveRecord::ConnectionAdapters::PostgreSQLAdapterTest#test_disable_extension_with_schema = 0.02 s = F

Failure:
ActiveRecord::ConnectionAdapters::PostgreSQLAdapterTest#test_disable_extension_with_schema [test/cases/adapters/postgresql/postgresql_adapter_test.rb:676]:
Expected: [["hstore"]]
  Actual: []

bin/test test/cases/adapters/postgresql/postgresql_adapter_test.rb:672

Finished in 0.070507s, 28.3659 runs/s, 56.7318 assertions/s.
2 runs, 4 assertions, 1 failures, 0 errors, 0 skips
```

Applied the same change for `test_disable_extension_without_schema`

Follow up rails#52528
Refer to rails#52452 (comment)

Author: yahonda

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

@@ -671,7 +671,8 @@ def test_date_decoding_disabled
 
       def test_disable_extension_with_schema
         @connection.execute("CREATE SCHEMA custom_schema")
-        @connection.execute("CREATE EXTENSION IF NOT EXISTS hstore SCHEMA custom_schema")
+        @connection.execute("DROP EXTENSION IF EXISTS hstore")
+        @connection.execute("CREATE EXTENSION hstore SCHEMA custom_schema")
         result = @connection.query("SELECT extname FROM pg_extension WHERE extnamespace = (SELECT oid FROM pg_namespace WHERE nspname = 'custom_schema')")
         assert_equal [["hstore"]], result.to_a
 
@@ -684,7 +685,8 @@ def test_disable_extension_with_schema
       end
 
       def test_disable_extension_without_schema
-        @connection.execute("CREATE EXTENSION IF NOT EXISTS hstore")
+        @connection.execute("DROP EXTENSION IF EXISTS hstore")
+        @connection.execute("CREATE EXTENSION hstore")
         result = @connection.query("SELECT extname FROM pg_extension")
         assert_includes result.to_a, ["hstore"]