[doc] update bips.md for 431

Author: glozow

doc/bips.md

@@ -69,3 +69,4 @@ BIPs that are implemented by Bitcoin Core:
   [`385`](https://github.com/bitcoin/bips/blob/master/bip-0385.mediawiki):
   Output Script Descriptors, and most of Script Expressions are implemented as of **v0.17.0** ([PR 13697](https://github.com/bitcoin/bitcoin/pull/13697)).
 * [`BIP 386`](https://github.com/bitcoin/bips/blob/master/bip-0386.mediawiki): tr() Output Script Descriptors are implemented as of **v22.0** ([PR 22051](https://github.com/bitcoin/bitcoin/pull/22051)).
+* [`BIP 431`](https://github.com/bitcoin/bips/blob/master/bip-0431.mediawiki): transactions with nVersion=3 are standard and treated as Topologically Restricted Until Confirmation as of **v28.0** ([PR 29496](https://github.com/bitcoin/bitcoin/pull/29496)).