Prepare release v1.21.0 (#1171)

Updates version and changelog for v1.21.0.

---------

Co-authored-by: Jacob Oaks <joaks@uber.com>

Author: garkhipov

CHANGELOG.md

@@ -10,11 +10,15 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## Unreleased
+## [1.21.0](https://github.com/uber-go/fx/compare/v1.20.1...v1.21.0) - 2024-03-13
 
 ### Added
 - fxtest: Add WithTestLogger option that uses a `testing.TB` as the
   Fx event logger.
+- An fxevent logger that can log events using a slog logger has been added.
+
+### Changed
+- Upgrade Dig dependency to v1.17.1
 
 ## [1.20.1](https://github.com/uber-go/fx/compare/v1.20.0...v1.20.1) - 2023-10-17
 

version.go

@@ -21,4 +21,4 @@
 package fx
 
 // Version is exported for runtime compatibility checks.
-const Version = "1.21.0-dev"
+const Version = "1.21.0"