[backport#12143] [Doc] Fix link for BIP-159 pull request

Summary:
91769d6e2 [Doc] Fix link for bip 159 pull request (azuchi)

Pull request description:

The link of the pull request for BIP-159 described in bips.md was a different link.

Backport of Core PR12143

Test Plan: read it

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D8204