Fix Python 3.8 SyntaxWarning: "is not" with a literal

### Description

Fixes this warning from Python 3.8 in `Query._set_entities`:

```
lib/sqlalchemy/orm/query.py:179: SyntaxWarning: "is not" with a literal. Did you mean "!="?
  if entities is not ():
```

Fixes #4938.

### Checklist

This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [x] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #4939
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4939
Pull-request-sha: 88167460ced7f576a9aed3d0ff0a6e7e18810004

Change-Id: I21464c3e69b4db6307db99f9ccb9b34bbac4e744

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index 92f9ee952..35416ae5e 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -176,7 +176,7 @@ class Query(Generative):
         self._primary_entity = None
         self._has_mapper_entities = False
 
-        if entities is not ():
+        if entities != ():
             for ent in util.to_list(entities):
                 entity_wrapper(self, ent)