Fixed issue with timedelta in heartbeat timer (PR #5987)

# Description

There seems to be an issue with the _set_timeout function of Tornado. If timeout is a timedelta with value zero it evaluates to false [here](https://github.com/tornadoweb/tornado/blob/master/tornado/queues.py#L62) which causes issues

# Self Check:

Strike through any lines that are not applicable (`~~line~~`) then check the box

- [ ] Attached issue to pull request
- [x] Changelog entry
- [ ] Type annotations are present
- [ ] Code is clear and sufficiently documented
- [ ] No (preventable) type errors (check using make mypy or make mypy-diff)
- [ ] Sufficient test cases (reproduces the bug/tests the requested feature)
- [ ] Correct, in line with design
- [ ] End user documentation is included or an issue is created for end-user documentation (add ref to issue here: )
- [ ] If this PR fixes a race condition in the test suite, also push the fix to the relevant stable branche(s) (see [test-fixes](https://internal.inmanta.com/development/core/tasks/build-master.html#test-fixes) for more info)

changelogs/unreleased/fix-issue-timedelta-heartbeat.yml

@@ -0,0 +1,3 @@
+description: Fixed issue with timedelta in heartbeat timer
+change-type: patch
+destination-branches: [master, iso6]

src/inmanta/server/protocol.py

@@ -502,8 +502,10 @@ async def get_calls(self, no_hang: bool) -> Optional[List[common.Request]]:
             if no_hang:
                 timeout = 0.1
             else:
-                timeout = self._interval
-
+                timeout = self._interval if self._interval > 0.1 else 0.1
+                # We choose to have a minimum of 0.1 as timeout as this is also the value used for no_hang.
+                # Furthermore, the timeout value cannot be zero as this causes an issue with Tornado:
+                # https://github.com/tornadoweb/tornado/issues/3271
             call = await self._queue.get(timeout=timedelta(seconds=timeout))
             if call is None:
                 # aborting session