4815f6e28b tried to de-duplicate bot
email addresses, but instead caused duplicates to crash:
```
Traceback (most recent call last):
File "./manage.py", line 157, in <module>
execute_from_command_line(sys.argv)
File "./manage.py", line 122, in execute_from_command_line
utility.execute()
File "/srv/zulip-venv-cache/56ac6adf406011a100282dd526d03537be84d23e/zulip-py3-venv/lib/python3.8/site-packages/django/core/management/__init__.py", line 413, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/srv/zulip-venv-cache/56ac6adf406011a100282dd526d03537be84d23e/zulip-py3-venv/lib/python3.8/site-packages/django/core/management/base.py", line 354, in run_from_argv
self.execute(*args, **cmd_options)
File "/srv/zulip-venv-cache/56ac6adf406011a100282dd526d03537be84d23e/zulip-py3-venv/lib/python3.8/site-packages/django/core/management/base.py", line 398, in execute
output = self.handle(*args, **options)
File "/home/zulip/deployments/2022-03-16-22-25-42/zerver/management/commands/convert_slack_data.py", line 59, in handle
do_convert_data(path, output_dir, token, threads=num_threads)
File "/home/zulip/deployments/2022-03-16-22-25-42/zerver/data_import/slack.py", line 1320, in do_convert_data
) = slack_workspace_to_realm(
File "/home/zulip/deployments/2022-03-16-22-25-42/zerver/data_import/slack.py", line 141, in slack_workspace_to_realm
) = users_to_zerver_userprofile(slack_data_dir, user_list, realm_id, int(NOW), domain_name)
File "/home/zulip/deployments/2022-03-16-22-25-42/zerver/data_import/slack.py", line 248, in users_to_zerver_userprofile
email = get_user_email(user, domain_name)
File "/home/zulip/deployments/2022-03-16-22-25-42/zerver/data_import/slack.py", line 406, in get_user_email
return SlackBotEmail.get_email(user["profile"], domain_name)
File "/home/zulip/deployments/2022-03-16-22-25-42/zerver/data_import/slack.py", line 85, in get_email
email_prefix += cls.duplicate_email_count[email]
TypeError: can only concatenate str (not "int") to str
```
Fix the stringification, make it case-insensitive, append with a dash
for readability, and add tests for all of the above.
2e50ead9d1