Update protocols/gossipsub/CHANGELOG.md

Co-authored-by: Elena Frank <[email protected]>

Author: jxs

protocols/gossipsub/CHANGELOG.md

@@ -1,6 +1,6 @@
 ## 0.50.0
 - Prevent mesh exceeding mesh_n_high when handling GRAFT messages.
-  See [PR XXXX](https://github.com/libp2p/rust-libp2p/pull/XXXX)
+  See [PR 6184](https://github.com/libp2p/rust-libp2p/pull/6184)
 
 - Fix underflow when shuffling peers after prunning.
   See [PR 6183](https://github.com/libp2p/rust-libp2p/pull/6183)