cockpit-ci: Update container to 2024-06-03

This also reverts the workaround introduced as part of 5d06c7d, now
fixed in the version of the typeshed that mypy is using.  See #20372.

Closes #20540

.cockpit-ci/container

@@ -1 +1 @@
-ghcr.io/cockpit-project/tasks:2024-04-25
+ghcr.io/cockpit-project/tasks:2024-06-03

src/cockpit/transports.py

@@ -402,8 +402,7 @@ def preexec_fn() -> None:
 
         super().__init__(loop, protocol, in_fd, out_fd)
 
-        # https://github.com/python/typeshed/pull/11548
-        self._get_watcher(loop).add_child_handler(self._process.pid, self._exited)  # type: ignore[arg-type]
+        self._get_watcher(loop).add_child_handler(self._process.pid, self._exited)
 
     def set_window_size(self, size: WindowSize) -> None:
         assert self._pty_fd is not None