Use notify 7.0.0 instead of a fork of 6.1.1

[musicinmybrain]

As @decathorpe noticed, notify-rs/notify@146b1bd appears to be the same as notify-rs/notify@0f87ab1 in the notify fork.

Therefore, it should be possible to use the released version of notify 7.0.0.

I tried this and got one test failure,

=================================================================================================== FAILURES ===================================================================================================
_________________________________________________________________________________________ test_awatch_interrupt_raise __________________________________________________________________________________________

self = <tests.test_watch.MockRustNotifyRaise object at 0x7ff6cadfbb60>, args = (1600, 50, 5000, <threading.Event at 0x7ff6ca55c9b0: set>)

    def watch(self, *args):
        if self.i == 1:
>           raise KeyboardInterrupt('test error')
E           KeyboardInterrupt: test error

tests/test_watch.py:204: KeyboardInterrupt
[…]

but this already happens for me on the current main, so this isn’t a regression.

This PR would resolve #312.