Fixes for flake8 (#1012)

Co-authored-by: Barret Schloerke <[email protected]>

shiny/_utils.py

@@ -393,7 +393,7 @@ def _step(fut: Optional["asyncio.Future[None]"] = None):
             assert fut.done()
             try:
                 fut.result()
-            except BaseException as e:
+            except BaseException as e:  # noqa: B036
                 exc = e
 
         if result_future.cancelled():
@@ -419,7 +419,7 @@ def _step(fut: Optional["asyncio.Future[None]"] = None):
         except (KeyboardInterrupt, SystemExit) as e:
             result_future.set_exception(e)
             raise
-        except BaseException as e:
+        except BaseException as e:  # noqa: B036
             result_future.set_exception(e)
         else:
             # If we get here, the coro didn't finish. Schedule it for completion.

shiny/render/renderer/_renderer.py

@@ -225,7 +225,9 @@ class AsyncValueFn(Generic[IT]):
 
     def __init__(self, fn: Callable[[], IT] | Callable[[], Awaitable[IT]]):
         if isinstance(fn, AsyncValueFn):
-            return cast(AsyncValueFn[IT], fn)
+            raise TypeError(
+                "Must not call `AsyncValueFn.__init__` with an object of class `AsyncValueFn`"
+            )
         self._is_async = is_async_callable(fn)
         self._fn = wrap_async(fn)
         self._orig_fn = fn