chore(core): improve `loop.Task` type annotation

diff --git a/core/src/trezor/ui/__init__.py b/core/src/trezor/ui/__init__.py
index 3aea331d..f4402a5c 100644
--- a/core/src/trezor/ui/__init__.py
+++ b/core/src/trezor/ui/__init__.py
@@ -149,12 +149,12 @@ class Layout(Generic[T]):
     def __init__(self, layout: LayoutObj[T]) -> None:
         """Set up a layout."""
         self.layout = layout
-        self.tasks: set[loop.Task] = set()
-        self.timers: dict[int, loop.Task] = {}
+        self.tasks: set[loop.Task[None]] = set()
+        self.timers: dict[int, loop.Task[None]] = {}
         self.result_box: loop.mailbox[Any] = loop.mailbox()
         self.button_request_ack_pending: bool = False
         self.button_request_box: loop.mailbox[ButtonRequest | None] = loop.mailbox()
-        self.button_request_task: loop.Task | None = None
+        self.button_request_task: loop.Task[None] | None = None
         self.transition_out: AttachType | None = None
         self.backlight_level = BacklightLevels.NORMAL
         self.context: Context | None = None
@@ -431,7 +431,7 @@ class Layout(Generic[T]):
         self.result_box.put(msg)
         raise Shutdown()
 
-    def create_tasks(self) -> Iterator[loop.Task]:
+    def create_tasks(self) -> Iterator[loop.Task[None]]:
         """Set up background tasks for a layout.
 
         Called from `start()`. Creates and yields a list of background tasks, typically
@@ -533,7 +533,7 @@ class Layout(Generic[T]):
             finally:
                 pm.close()
 
-    def _task_finalizer(self, task: loop.Task, value: Any) -> None:
+    def _task_finalizer(self, task: loop.Task[None], value: Any) -> None:
         if value is None:
             # all is good
             if __debug__:
@@ -559,7 +559,7 @@ class Layout(Generic[T]):
         if __debug__:
             log.error(__name__, "UI task returned non-None: %s (%s)", task, value)
 
-    def _start_task(self, task: loop.Task) -> None:
+    def _start_task(self, task: loop.Task[None]) -> None:
         self.tasks.add(task)
         loop.schedule(task, finalizer=self._task_finalizer)
 
diff --git a/core/src/trezor/ui/layouts/homescreen.py b/core/src/trezor/ui/layouts/homescreen.py
index b54efb4d..de9adc13 100644
--- a/core/src/trezor/ui/layouts/homescreen.py
+++ b/core/src/trezor/ui/layouts/homescreen.py
@@ -49,7 +49,7 @@ class UsbAwareLayout(ui.Layout):
             event = await usbcheck
             self._event(self.layout.usb_event, event)
 
-    def create_tasks(self) -> Iterator[loop.Task]:
+    def create_tasks(self) -> Iterator[loop.Task[None]]:
         yield from super().create_tasks()
         yield self.usb_checker_task()
 
diff --git a/core/src/trezor/workflow.py b/core/src/trezor/workflow.py
index 7540af85..d13c689c 100644
--- a/core/src/trezor/workflow.py
+++ b/core/src/trezor/workflow.py
@@ -49,7 +49,7 @@ tasks: set[loop.spawn] = set()
 default_task: loop.spawn | None = None
 
 # Constructor for the default workflow.  Returns a workflow task.
-default_constructor: Callable[[], loop.Task] | None = None
+default_constructor: Callable[[], loop.Task[None]] | None = None
 
 # Determines whether idle timer firing closes currently running workflow. Storage is locked always.
 autolock_interrupts_workflow: bool = True
@@ -127,7 +127,10 @@ def start_default() -> None:
     autolock_interrupts_workflow = True
 
 
-def set_default(constructor: Callable[[], loop.Task], restart: bool = False) -> None:
+def set_default(
+    constructor: Callable[[], loop.Task[None]],
+    restart: bool = False,
+) -> None:
     """Configure a default workflow, which will be started next time it is needed."""
     global default_constructor
     if __debug__:
@@ -206,7 +209,7 @@ class IdleTimer:
 
     def __init__(self) -> None:
         self.timeouts: dict[IdleCallback, int] = {}
-        self.tasks: dict[IdleCallback, loop.Task] = {}
+        self.tasks: dict[IdleCallback, loop.Task[None]] = {}
 
     async def _timeout_task(self, callback: IdleCallback) -> None:
         # This function is async, so the result of self._timeout_task() is an awaitable,