Fix CHANGELOG of 0.60.0 (#3925)

The change `* Autoharness Subcommand by @carolynzech in
https://github.com/model-checking/kani/pull/3874` should be of Major
Changes instead of Breaking Changes.

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under the terms of the Apache 2.0 and MIT licenses.

Author: qinheping

CHANGELOG.md

@@ -7,9 +7,11 @@ This file was introduced starting Kani 0.23.0, so it only contains changes from
 ## [0.60.0]
 
 ### Breaking Changes
-* Autoharness Subcommand by @carolynzech in https://github.com/model-checking/kani/pull/3874
 * Remove Ubuntu 20.04 CI usage by @tautschnig in https://github.com/model-checking/kani/pull/3918
 
+### Major Changes
+* Autoharness Subcommand by @carolynzech in https://github.com/model-checking/kani/pull/3874
+
 ### What's Changed
 * Fast fail option - Stop verification process as soon as one failure is observed by @rajath-mk in https://github.com/model-checking/kani/pull/3879
 * Fail verification for UB regardless of whether `#[should_panic]` is enabled by @tautschnig in https://github.com/model-checking/kani/pull/3860