fix: use lock while fetching email changes

[s-aga-r]

Traceback with variables (most recent call last):
  File "apps/mail/mail/api/jmap.py", line 36, in push_notification
    enqueue_fetch_changes(account, state)
      account = 'notifications@frappecloud.com'
      request_data = {'@type': 'StateChange', 'changed': {'it': {'Thread': 'sv7ura', 'Mailbox': 'sv7ura', 'Email': 'sv7ura'}}}
      changes = [{'Thread': 'sv7ura', 'Mailbox': 'sv7ura', 'Email': 'sv7ura'}]
      change = {'Thread': 'sv7ura', 'Mailbox': 'sv7ura', 'Email': 'sv7ura'}
      key = ********
      state = 'sv7ura'
  File "apps/mail/mail/mail/doctype/email_message/email_message.py", line 1189, in enqueue_fetch_changes
    enqueue_job(
      account = 'notifications@frappecloud.com'
      email_state = 'sv7ura'
      job_id = 'fetch_changes:notifications@frappecloud.com'
  File "apps/mail/mail/utils/__init__.py", line 185, in enqueue_job
    frappe.enqueue(method, job_id=job_id, deduplicate=deduplicate, **kwargs)
      method = <function fetch_changes at 0x7f4b3c156c00>
      job_id = 'fetch_changes:notifications@frappecloud.com'
      deduplicate = True
      kwargs = {'account': 'notifications@frappecloud.com', 'email_state': 'sv7ura', 'queue': 'short', 'enqueue_after_commit': True}
  File "apps/frappe/frappe/utils/background_jobs.py", line 128, in enqueue
    job.delete()
      method = <function fetch_changes at 0x7f4b3c156c00>
      queue = 'short'
      timeout = None
      event = None
      is_async = True
      job_name = None
      now = False
      enqueue_after_commit = True
      on_success = None
      on_failure = None
      at_front = False
      job_id = 'fetch_changes:notifications@frappecloud.com'
      deduplicate = True
      at_front_when_starved = False
      kwargs = {'account': 'notifications@frappecloud.com', 'email_state': 'sv7ura'}
      job = <Job frappemail.frappe.cloud||fetch_changes|notifications@frappecloud.com: frappe.utils.background_jobs.execute_job(event=None, is_async=True, job_name='mail.mail.doctype.email_message.email_message.fetch_changes', kwargs={'account': 'notifications@frappecloud.com', 'email_state': 'svoura'}, method=<function fetch_changes at 0x7f4b3cfd4e00>, site='frappemail.frappe.cloud', user='Administrator')>
  File "env/lib/python3.11/site-packages/rq/job.py", line 1319, in delete
    self._remove_from_registries(pipeline=pipeline, remove_from_queue=remove_from_queue)
      self = <Job frappemail.frappe.cloud||fetch_changes|notifications@frappecloud.com: frappe.utils.background_jobs.execute_job(event=None, is_async=True, job_name='mail.mail.doctype.email_message.email_message.fetch_changes', kwargs={'account': 'notifications@frappecloud.com', 'email_state': 'svoura'}, method=<function fetch_changes at 0x7f4b3cfd4e00>, site='frappemail.frappe.cloud', user='Administrator')>
      pipeline = None
      remove_from_queue = True
      delete_dependents = False
      connection = <redis.client.Redis(<redis.connection.ConnectionPool(<redis.connection.Connection(host=localhost,port=11000,db=0)>)>)>
  File "env/lib/python3.11/site-packages/rq/job.py", line 1261, in _remove_from_registries
    if self.is_finished:
      self = <Job frappemail.frappe.cloud||fetch_changes|notifications@frappecloud.com: frappe.utils.background_jobs.execute_job(event=None, is_async=True, job_name='mail.mail.doctype.email_message.email_message.fetch_changes', kwargs={'account': 'notifications@frappecloud.com', 'email_state': 'svoura'}, method=<function fetch_changes at 0x7f4b3cfd4e00>, site='frappemail.frappe.cloud', user='Administrator')>
      pipeline = None
      remove_from_queue = True
      BaseRegistry = rq.registry.BaseRegistry
      Queue = rq.queue.Queue
      q = <Queue home-frappe-frappe-bench:short>
  File "env/lib/python3.11/site-packages/rq/job.py", line 442, in is_finished
    return self.get_status() == JobStatus.FINISHED
      self = <Job frappemail.frappe.cloud||fetch_changes|notifications@frappecloud.com: frappe.utils.background_jobs.execute_job(event=None, is_async=True, job_name='mail.mail.doctype.email_message.email_message.fetch_changes', kwargs={'account': 'notifications@frappecloud.com', 'email_state': 'svoura'}, method=<function fetch_changes at 0x7f4b3cfd4e00>, site='frappemail.frappe.cloud', user='Administrator')>
  File "env/lib/python3.11/site-packages/rq/job.py", line 410, in get_status
    raise InvalidJobOperation(f'Failed to retrieve status for job: {self.id}')
      self = <Job frappemail.frappe.cloud||fetch_changes|notifications@frappecloud.com: frappe.utils.background_jobs.execute_job(event=None, is_async=True, job_name='mail.mail.doctype.email_message.email_message.fetch_changes', kwargs={'account': 'notifications@frappecloud.com', 'email_state': 'svoura'}, method=<function fetch_changes at 0x7f4b3cfd4e00>, site='frappemail.frappe.cloud', user='Administrator')>
      refresh = True
      status = None
rq.exceptions.InvalidJobOperation: Failed to retrieve status for job: frappemail.frappe.cloud||fetch_changes|notifications@frappecloud.com