Fix link to proposal

Author: calda

CHANGELOG.md

@@ -9118,6 +9118,7 @@ Swift 1.0
 [SE-0336]: <https://github.com/apple/swift-evolution/blob/main/proposals/0336-distributed-actor-isolation.md>
 [SE-0343]: <https://github.com/apple/swift-evolution/blob/main/proposals/0343-top-level-concurrency.md>
 [SE-0340]: <https://github.com/apple/swift-evolution/blob/main/proposals/0340-swift-noasync.md>
+[SE-0345]: <https://github.com/apple/swift-evolution/blob/main/proposals/0345-if-let-shorthand.md>
 
 [SR-75]: <https://bugs.swift.org/browse/SR-75>
 [SR-106]: <https://bugs.swift.org/browse/SR-106>