Patch supports_statement_cache warning. (#259)

* patch fixing SQLAlchemy 'supports_statement_cache' warning. SQLAlchemy implementation looks into the class dictionary which is why the warning is still present even though flag is set on the Mixin base classes. The value is properly set into the base classes now.

* Update CHANGES.rst

Co-authored-by: Brooke White <Brooke-white@users.noreply.github.com>

CHANGES.rst

@@ -1,7 +1,7 @@
 0.8.12 (unreleased)
 -------------------
 
-- Nothing changed yet.
+- Fix SQLAlchemy's "supports_statement_cache" (`Pull #259 <https://github.com/sqlalchemy-redshift/sqlalchemy-redshift/pull/259>`_)
 
 
 0.8.11 (2022-07-27)

sqlalchemy_redshift/dialect.py

@@ -558,9 +558,6 @@ class RedshiftDialectMixin(DefaultDialect):
 
     name = 'redshift'
     max_identifier_length = 127
-    # explicitly disables statement cache to disable warnings in logs
-    # ref: https://docs.sqlalchemy.org/en/14/core/connections.html#caching-for-third-party-dialects  # noqa
-    supports_statement_cache = False
 
     statement_compiler = RedshiftCompiler
     ddl_compiler = RedshiftDDLCompiler
@@ -1036,7 +1033,7 @@ def dbapi(cls):
 class RedshiftDialect_psycopg2(
     Psycopg2RedshiftDialectMixin, PGDialect_psycopg2
 ):
-    pass
+    supports_statement_cache = False
 
 
 # Add RedshiftDialect synonym for backwards compatibility.
@@ -1046,7 +1043,7 @@ class RedshiftDialect_psycopg2(
 class RedshiftDialect_psycopg2cffi(
     Psycopg2RedshiftDialectMixin, PGDialect_psycopg2cffi
 ):
-    pass
+    supports_statement_cache = False
 
 
 class RedshiftDialect_redshift_connector(RedshiftDialectMixin, PGDialect):