Dialect: Fix get_pk_constraint to return list instead of set type

The test suite of `meltano-tap-cratedb`, derived from the corresponding
PostgreSQL adapter, will process database introspection return values by
marshalling them to JSON. Because `get_pk_constraint` returns a `set`
type, that will fail.

    TypeError: Object of type set is not JSON serializable

CHANGES.md

@@ -5,6 +5,7 @@
 - Added/reactivated documentation as `sqlalchemy-cratedb`
 - Added `CrateIdentifierPreparer`, in order to quote reserved words
   like `object` properly, for example when used as column names.
+- Fixed `CrateDialect.get_pk_constraint` to return `list` instead of `set` type
 
 ## 2024/06/13 0.37.0
 - Added support for CrateDB's [FLOAT_VECTOR] data type and its accompanying

src/sqlalchemy_cratedb/dialect.py

@@ -340,7 +340,7 @@ def result_fun(result):
             (table_name, schema or self.default_schema_name)
         )
         pks = result_fun(pk_result)
-        return {'constrained_columns': pks,
+        return {'constrained_columns': list(sorted(pks)),
                 'name': 'PRIMARY KEY'}
 
     @reflection.cache

tests/dialect_test.py

@@ -88,7 +88,7 @@ def test_primary_keys_2_3_0(self):
         )
         self.fake_cursor.fetchall = MagicMock(return_value=[["id"], ["id2"], ["id3"]])
 
-        eq_(insp.get_pk_constraint("characters")['constrained_columns'], {"id", "id2", "id3"})
+        eq_(insp.get_pk_constraint("characters")['constrained_columns'], ["id", "id2", "id3"])
         self.fake_cursor.fetchall.assert_called_once_with()
         in_("information_schema.key_column_usage", self.executed_statement)
         in_("table_catalog = ?", self.executed_statement)
@@ -103,7 +103,7 @@ def test_primary_keys_3_0_0(self):
         )
         self.fake_cursor.fetchall = MagicMock(return_value=[["id"], ["id2"], ["id3"]])
 
-        eq_(insp.get_pk_constraint("characters")['constrained_columns'], {"id", "id2", "id3"})
+        eq_(insp.get_pk_constraint("characters")['constrained_columns'], ["id", "id2", "id3"])
         self.fake_cursor.fetchall.assert_called_once_with()
         in_("information_schema.key_column_usage", self.executed_statement)
         in_("table_schema = ?", self.executed_statement)