When task assignees have more than one task at the same time in field service, 
and tries to remove the planned date from one of the tasks,
A traceback will appear.

Steps to reproduce the error:
- Go to Field Service > Create a new task with the planned date and Assignees
- Create another task with the same planned date and Assignees > Save
- Now try to remove the planned date

Traceback:
```
AttributeError: 'bool' object has no attribute 'tzinfo'
  File "odoo/http.py", line 2254, in __call__
    response = request._serve_db()
  File "odoo/http.py", line 1829, in _serve_db
    return self._transactioning(_serve_ir_http, readonly=ro)
  File "odoo/http.py", line 1849, in _transactioning
    return service_model.retrying(func, env=self.env)
  File "odoo/service/model.py", line 134, in retrying
    result = func()
  File "odoo/http.py", line 1827, in _serve_ir_http
    return self._serve_ir_http(rule, args)
  File "odoo/http.py", line 1834, in _serve_ir_http
    response = self.dispatcher.dispatch(rule.endpoint, args)
  File "odoo/http.py", line 2059, in dispatch
    result = self.request.registry['ir.http']._dispatch(endpoint)
  File "odoo/addons/base/models/ir_http.py", line 220, in _dispatch
    result = endpoint(**request.params)
  File "odoo/http.py", line 740, in route_wrapper
    result = endpoint(self, *args, **params_ok)
  File "addons/web/controllers/dataset.py", line 38, in call_kw
    return self._call_kw(model, method, args, kwargs)
  File "addons/web/controllers/dataset.py", line 34, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "odoo/api.py", line 458, in call_kw
    result = getattr(recs, name)(*args, **kwargs)
  File "addons/web/models/models.py", line 1011, in onchange
    todo = [
  File "addons/web/models/models.py", line 1014, in <listcomp>
    if field_name not in done and snapshot0.has_changed(field_name)
  File "addons/web/models/models.py", line 1127, in has_changed
    return self[field_name] != self.record[field_name]
  File "odoo/models.py", line 6608, in __getitem__
    return self._fields[key].__get__(self, self.env.registry[self._name])
  File "odoo/fields.py", line 1261, in __get__
    self.compute_value(recs)
  File "odoo/fields.py", line 1443, in compute_value
    records._compute_field_value(self)
  File "addons/mail/models/mail_thread.py", line 416, in _compute_field_value
    return super()._compute_field_value(field)
  File "odoo/models.py", line 4934, in _compute_field_value
    fields.determine(field.compute, self)
  File "odoo/fields.py", line 100, in determine
    return needle(*args)
  File "home/odoo/src/enterprise/saas-17.2/project_enterprise/models/project_task.py", line 227, in _compute_planning_overlap
    absolute_min_start = utc.localize(self[0].planned_date_begin)
  File "__init__.py", line 257, in localize
    if dt.tzinfo is not None:
```

https://github.com/odoo/enterprise/blob/74e8fa829cf17677ddcb29d91a0521d5d5b9a1b6/project_enterprise/models/project_task.py#L229-L230 When the user removes the planned date,
"planned_date_begin" and "date_deadline" will be False.
So it will lead to the above traceback.

sentry-5444639133