docs(unstable): Correct stabilization version for MSRV-resolver

Author: epage

src/doc/src/reference/unstable.md

@@ -359,7 +359,7 @@ This was stabilized in 1.79 in [#13608](https://github.com/rust-lang/cargo/pull/
 
 ### MSRV-aware resolver
 
-This was stabilized in 1.83 in [#14639](https://github.com/rust-lang/cargo/pull/14639).
+This was stabilized in 1.84 in [#14639](https://github.com/rust-lang/cargo/pull/14639).
 
 ### Convert `incompatible_toolchain` error into a lint