📋 Update changelog

Author: matteosecli

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased](https://github.com/qutip/QuantumToolbox.jl/tree/main)
 
+- Check for orthogonality breakdown in `Lanczos` solver for `spectrum`. ([#501])
+
 ## [v0.32.1]
 Release date: 2025-06-24
 
@@ -253,3 +255,4 @@ Release date: 2024-11-13
 [#487]: https://github.com/qutip/QuantumToolbox.jl/issues/487
 [#489]: https://github.com/qutip/QuantumToolbox.jl/issues/489
 [#494]: https://github.com/qutip/QuantumToolbox.jl/issues/494
+[#501]: https://github.com/qutip/QuantumToolbox.jl/issues/501