fix(migration): replace unquote with double percentages (apache#30532)

(cherry picked from commit 163b71e)

superset/migrations/env.py

@@ -16,7 +16,6 @@
 # under the License.
 import logging
 import time
-import urllib.parse
 from logging.config import fileConfig
 
 from alembic import context
@@ -43,8 +42,9 @@
         "SQLite Database support for metadata databases will \
         be removed in a future version of Superset."
     )
-decoded_uri = urllib.parse.unquote(DATABASE_URI)
-config.set_main_option("sqlalchemy.url", decoded_uri)
+# Escape % chars in the database URI to avoid interpolation errors in ConfigParser
+escaped_uri = DATABASE_URI.replace("%", "%%")
+config.set_main_option("sqlalchemy.url", escaped_uri)
 target_metadata = Base.metadata  # pylint: disable=no-member