Using explain to get the approximate count with distributed tables

I am using `explain` on queries to get the approximate count of a query. When the tables are distributed with citus, I am getting this following error

```
Traceback (most recent call last):
File "/Users/noor/.virtualenvs/app/lib/python3.8/site-packages/django/db/backends/utils.py", line 85, in _execute
return self.cursor.execute(sql, params)
psycopg2.errors.InternalError_: cannot switch local execution status from local execution required to local execution disabled since it can cause visibility problems in the current transaction

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "/src/main/queryset_fn.py", line 191, in estimated_count
return qs.count(), False
File "/Users/noor/.virtualenvs/app/lib/python3.8/site-packages/django/db/models/query.py", line 412, in count
return self.query.get_count(using=self.db)
File "/Users/noor/.virtualenvs/app/lib/python3.8/site-packages/django/db/models/sql/query.py", line 528, in get_count
number = obj.get_aggregation(using, ['__count'])['__count']
File "/Users/noor/.virtualenvs/app/lib/python3.8/site-packages/django/db/models/sql/query.py", line 513, in get_aggregation
result = compiler.execute_sql(SINGLE)
File "/Users/noor/.virtualenvs/app/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1175, in execute_sql
cursor.execute(sql, params)
File "/Users/noor/.virtualenvs/app/lib/python3.8/site-packages/django/db/backends/utils.py", line 66, in execute
return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
File "/Users/noor/.virtualenvs/app/lib/python3.8/site-packages/django/db/backends/utils.py", line 75, in _execute_with_wrappers
return executor(sql, params, many, context)
File "/Users/noor/.virtualenvs/app/lib/python3.8/site-packages/django/db/backends/utils.py", line 85, in _execute
return self.cursor.execute(sql, params)
File "/Users/noor/.virtualenvs/app/lib/python3.8/site-packages/django/db/utils.py", line 90, in __exit__
raise dj_exc_value.with_traceback(traceback) from exc_value
File "/Users/noor/.virtualenvs/app/lib/python3.8/site-packages/django/db/backends/utils.py", line 85, in _execute
return self.cursor.execute(sql, params)
django.db.utils.InternalError: cannot switch local execution status from local execution required to local execution disabled since it can cause visibility problems in the current transaction
```

the estimated count function look like this

```
def _estimate_count(queryset: models.QuerySet) -> Optional[int]:
lines = queryset.only("pk").explain(format="json")
if isinstance(lines, str):
lines = ast.literal_eval(lines) # turn to dict
if isinstance(lines, list) and lines:
return lines[0]["Plan"]["Plan Rows"]
return None
```

The queryset can be something as simple as `Model.objects.filter()` . It seems when estimate is used with other queries, this error is raised. It is also happening during tests.

Start by reproducing the failure with the `_estimate_count` function in `/src/main/queryset_fn.py` and a simple `Model.objects.filter()` queryset using `explain(format="json")`. Inspect how django-multitenant handles distributed-table queries and the tests that call this estimation path. Done means the estimate no longer raises the reported transaction error during normal queries and tests.

Written by the indexing model from the issue text.