Add missing version number to changelog (#3877)

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CHANGELOG.md

@@ -4,6 +4,8 @@ This file contains notable changes (e.g. breaking changes, major changes, etc.)
 
 This file was introduced starting Kani 0.23.0, so it only contains changes from version 0.23.0 onwards.
 
+## [0.59.0]
+
 ## Breaking Changes
 * Deprecate `--enable-unstable` and `--restrict-vtable` by @celinval in https://github.com/model-checking/kani/pull/3859
 * Do not report arithmetic overflow for floating point operations that produce +/-Inf by @rajath-mk in https://github.com/model-checking/kani/pull/3873