Update reference/generics.html with PEP695 type parameter syntax

[jason-sachs]

The typing documentation for generics is somewhat inconsistent in the use of new syntax:

• Generics — typing documentation (https://typing.python.org/en/latest/reference/generics.html) doesn’t include the new syntax class Foo[T] at all

• Generics — typing documentation (https://typing.python.org/en/latest/spec/generics.html) does, and mentions PEP695

Are there any plans on updating reference/generics.html? It is a bit confusing for someone who is using Python 3.12 or newer to see out-of-date information.

[JelleZijlstra]

Yes, we should update the reference page to use PEP 695 now that Python 3.12 is a few years old.