Bokeh service does not start when using processes=False

The bokeh service does not start on Debian when using `processes=False`. Strangely, it does start on macOS.

Minimal reproducing example:
```python
from distributed import LocalCluster, Client

cluster = LocalCluster(processes=False)
client = Client(cluster)
print(client.scheduler_info()))
client.close()
```

On macOS with distributed 1.22.0, the output is:
```json
{
"type": "Scheduler",
"id": "Scheduler-275f860b-d0cd-46a8-865a-c75b8ebd6fc8",
"address": "inproc://10.40.36.245/56255/1",
"services": {
"bokeh": 8787
},
"workers": {
"inproc://10.40.36.245/56255/2": {
"name": "inproc://10.40.36.245/56255/2",
"memory_limit": 17179869184,
"host": "10.40.36.245",
"resources": {},
"ncores": 8,
"services": {
"bokeh": 61024
},
"local_directory": "/Users/laurent/[...]/dask-worker-space/worker-bh9f2yjh",
"pid": 56255,
"cpu": 0,
"memory": 100495360,
"time": 1.53373248E9,
"read_bytes": 0,
"write_bytes": 0,
"num_fds": 68
}
}
}
```

While running the same code on Debian (in a Docker container with no other processes running) results in the below output. Notice that on Debian, the `"services"` value is an empty dict! With `processes=True`, the bokeh service does start.
```json
{
"type": "Scheduler",
"id": "Scheduler-fd83c67d-515a-499f-9c1c-fd9641d54d51",
"address": "inproc://172.18.0.2/104/1",
"services": {},
"workers": {
"inproc://172.18.0.2/104/2": {
"name": "inproc://172.18.0.2/104/2",
"memory_limit": 12575559680,
"host": "172.18.0.2",
"resources": {},
"ncores": 6,
"services": {
"bokeh": 41839
},
"local_directory": "/[...]/dask-worker-space/worker-0yv06g56",
"pid": 104,
"cpu": 0,
"memory": 112869376,
"time": 1.53373286E9,
"read_bytes": 0,
"write_bytes": 0,
"num_fds": 24
}
}
}
```