Apply suggestions from code review

Co-authored-by: Ronnie Dutta <61982285+MetRonnie@users.noreply.github.com>

cylc/flow/platforms.py

@@ -302,7 +302,7 @@ def get_platform_from_group(
     else:
         platform_names = group['platforms']
 
-    # Return False if there are no platforms available to be selected.
+    # If there are no platforms available to be selected:
     if not platform_names:
         hosts_consumed = [
             host

cylc/flow/task_job_mgr.py

@@ -36,7 +36,7 @@
 )
 from shutil import rmtree
 from time import time
-from typing import TYPE_CHECKING, Any, Union, Optional
+from typing import TYPE_CHECKING, Any, List, Union, Optional
 
 from cylc.flow import LOG
 from cylc.flow.job_runner_mgr import JobPollContext
@@ -230,7 +230,7 @@ def prep_submit_task_jobs(self, workflow, itasks, check_syntax=True):
         """
         prepared_tasks = []
         bad_tasks = []
-        out_of_hosts_tasks: list = []
+        out_of_hosts_tasks: List[TaskProxy] = []
         for itask in itasks:
             if not itask.state(TASK_STATUS_PREPARING):
                 # bump the submit_num *before* resetting the state so that the
@@ -288,10 +288,8 @@ def submit_task_jobs(self, workflow, itasks, curve_auth,
             auth_itasks.setdefault(platform_name, [])
             auth_itasks[platform_name].append(itask)
         # Submit task jobs for each platform
-        done_tasks = bad_tasks
-
-        # Out of host tasks can be considered done for now:
-        [done_tasks.append(itask) for itask in out_of_hosts_tasks]
+        # Non-prepared tasks can be considered done for now:
+        done_tasks = [*bad_tasks, *out_of_hosts_tasks]
 
         for _, itasks in sorted(auth_itasks.items()):
             # Find the first platform where >1 host has not been tried and