Update link to `Categorical._codes` removal in 2.0 what's new doc
Currently this is pointing to the PR where `Categorical._codes` was deprecated in `pandas=1.3` (https://github.com/pandas-dev/pandas/pull/41429) instead of the PR where it was removed for `pandas=2.0` (https://github.com/pandas-dev/pandas/pull/49258)
I think we point to the deprecation prs in general. Ah, happy to close this PR if it's against an agreed upon standard practice. FWIW I will say I found it confusing as the PR wasn't consistent text in the changelog entry.  Yeah we typically link to the PR that introduces the deprecation (which hopefully links to the PR that enforces the deprecation)