proposal: allow passing type parameterized channels of different element types to "close".

[zigo101]

The spec says:

If the type of the argument to close is a type parameter, all types in its type set must be channels with the same element type.

But the code compiles (since 1.18):

func dig[T ~chan int | ~chan bool | ~chan<- string](x T) {
	close(x)
}

So maybe it is a good idea to just remove the about quoted line from spec.