Assign SE-0481 to the weak let proposal and put it in review

Author: rjmccall

proposals/NNNN-weak-let.md renamed to proposals/0481-weak-let.md

@@ -1,11 +1,10 @@
 # Feature name
 
-* Proposal: [SE-NNNN](NNNN-weak-let.md)
+* Proposal: [SE-0481](0481-weak-let.md)
 * Authors: [Mykola Pokhylets](https://github.com/nickolas-pohilets)
 * Review Manager: [John McCall](https://github.com/rjmccall)
-* Status: **Awaiting review**
+* Status: **Active review (April 30th...May 13th, 2025)**
 * Implementation: [swiftlang/swift#80440](https://github.com/swiftlang/swift/pull/80440)
-* Upcoming Feature Flag: `WeakLet`
 * Review: ([discussion](https://forums.swift.org/t/weak-captures-in-sendable-sending-closures/78498)) ([pitch](https://forums.swift.org/t/pitch-weak-let/79271))
 
 [SE-0302]: https://github.com/swiftlang/swift-evolution/blob/main/proposals/0302-concurrent-value-and-concurrent-closures.md