tour: The note about deterministic execution is not actual anymore with automatic seeds starting from Go 1.20

[mrhakimov]

Context: https://go.dev/tour/basics/1

According to the Go 1.20 Release Notes:

The math/rand package now automatically seeds the global random number generator with a random value

So, the note from the tour:

Note: The environment in which these programs are executed is deterministic, so each time you run the example program rand.Intn will return the same number.

(To see a different number, seed the number generator; see [rand.Seed](https://go.dev/pkg/math/rand/#Seed). Time is constant in the playground, so you will need to use something else as the seed.)

is not actual anymore

[crisman]

Same as #1448, can be closed.

Fixed in golang/website#194