fix: add plain postgres alias (#21045)

setup.py

@@ -64,10 +64,11 @@ def get_git_sha() -> str:
     zip_safe=False,
     entry_points={
         "console_scripts": ["superset=superset.cli.main:superset"],
-        # the `postgres+psycopg2://` scheme was removed in SQLAlchemy 1.4, add an alias here
-        # to prevent breaking existing databases
+        # the `postgres` and `postgres+psycopg2://` schemes were removed in SQLAlchemy 1.4
+        # add an alias here to prevent breaking existing databases
         "sqlalchemy.dialects": [
-            "postgres.psycopg2=sqlalchemy.dialects.postgresql:dialect"
+            "postgres.psycopg2 = sqlalchemy.dialects.postgresql:dialect",
+            "postgres = sqlalchemy.dialects.postgresql:dialect",
         ],
     },
     install_requires=[