DOC: Link to SPEC 0 instead of NEP 29

[Aloqeely]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

https://pandas.pydata.org/docs/development/policies.html#python-support

Documentation problem

NEP 29 has been superseded by SPEC 0

Suggested fix for documentation

We should link to SPEC 0 instead.

[tilovashahrin]

Hello, I want to tackle this issue and see if I can contribute!

[Aloqeely]

@tilovashahrin sure, go ahead!