pybind/mgr: pin cheroot version in requirements-required.txt

pybind/mgr: pin cheroot version in requirements-required.txt

With python 3.10 (didn't seem to happen with python 3.12) the
pybind/mgr/cephadm/tests/test_node_proxy.py test times out.
This appears to be related to a new release of the cheroot
package and a github issues describing the same problem
we're seeing has been opened by another user
https://github.com/cherrypy/cheroot/issues/769

It is worth noting that the workaround described in that
issue does also work for us. If you add

```
import cheroot
cheroot.server.HTTPServer._serve_unservicable = lambda: None
```

after the existing imports in test_node_proxy.py the
test hanging issue also disappears. Also worth noting the
particular pin of

cheroot~=10.0

was chosen as it matches the existing pin being used
in pybind/mgr/dashboard/constraints.txt

Signed-off-by: Adam King <adking@redhat.com>