Be explicit about filesystem monitoring radio being ForkProcess (#3680)

Prior to this PR, on Linux, this is already a fork process because of
defaults.

But this process *must* be a fork process, for the same reason that
other explicit ForkProcesses in Parsl must be fork processes: we cannot
re-import the the unknown user workflow script again.

This PR makes that explicit and consistent with other forked processes.

Longer term, multiprocessing-forked processes need to go away throughout
Parsl - see issue #2343, but this PR is not for that.

# Changed Behaviour

This should not change behaviour on Linux. On platforms that are not
Linux, nothing is supported and is probably already broken here.

## Type of change

- Code maintenance/cleanup

parsl/monitoring/monitoring.py

@@ -6,7 +6,7 @@
 import pickle
 import queue
 import time
-from multiprocessing import Event, Process
+from multiprocessing import Event
 from multiprocessing.queues import Queue
 from typing import TYPE_CHECKING, Literal, Optional, Tuple, Union, cast
 
@@ -171,11 +171,11 @@ def start(self, dfk_run_dir: str, config_run_dir: Union[str, os.PathLike]) -> No
         self.dbm_proc.start()
         logger.info("Started the router process %s and DBM process %s", self.router_proc.pid, self.dbm_proc.pid)
 
-        self.filesystem_proc = Process(target=filesystem_receiver,
-                                       args=(self.logdir, self.resource_msgs, dfk_run_dir),
-                                       name="Monitoring-Filesystem-Process",
-                                       daemon=True
-                                       )
+        self.filesystem_proc = ForkProcess(target=filesystem_receiver,
+                                           args=(self.logdir, self.resource_msgs, dfk_run_dir),
+                                           name="Monitoring-Filesystem-Process",
+                                           daemon=True
+                                           )
         self.filesystem_proc.start()
         logger.info("Started filesystem radio receiver process %s", self.filesystem_proc.pid)