Add migration to change environment_roles role column from string to

enum type.
Fix tests and functions affected by the column type change.

atst/routes/applications/settings.py

@@ -99,7 +99,7 @@ def filter_env_roles_form_data(member, environments):
 
         if len(env_roles_set) == 1:
             (env_role,) = env_roles_set
-            env_data["role"] = env_role.role
+            env_data["role"] = env_role.role.name
             env_data["disabled"] = env_role.disabled
 
         env_roles_form_data.append(env_data)