database: fix migration for mysql.

- It's really nice that mysql fails on that dependening on version, and our CI doesn't catch that.

rhodecode/lib/dbmigrate/versions/097_version_4_17_0.py

@@ -1,35 +1,36 b''
 # -*- coding: utf-8 -*-
 
 import logging
 
 from alembic.migration import MigrationContext
 from alembic.operations import Operations
+from sqlalchemy import String
 
 from rhodecode.lib.dbmigrate.versions import _reset_base
 from rhodecode.model import init_model_encryption
 
 
 log = logging.getLogger(__name__)
 
 
 def upgrade(migrate_engine):
     """
     Upgrade operations go here.
     Don't create your own engine; bind migrate_engine to your metadata
     """
     _reset_base(migrate_engine)
     from rhodecode.lib.dbmigrate.schema import db_4_16_0_2
 
     init_model_encryption(db_4_16_0_2)
 
     context = MigrationContext.configure(migrate_engine.connect())
     op = Operations(context)
 
     repo_group = db_4_16_0_2.RepoGroup.__table__
 
     with op.batch_alter_table(repo_group.name) as batch_op:
-        batch_op.alter_column("repo_group_name_hash", nullable=False)
+        batch_op.alter_column("repo_group_name_hash", type_=String(1024), nullable=False)
 
 
 def downgrade(migrate_engine):
     pass