Update Optimization requirement to 4.0.0 in /docs

Updates the requirements on [Optimization](https://github.com/SciML/Optimization.jl) to permit the latest version.
- [Release notes](https://github.com/SciML/Optimization.jl/releases)
- [Changelog](https://github.com/SciML/Optimization.jl/blob/master/NEWS.md)
- [Commits](SciML/Optimization.jl@v0.1.1...v4.0.0)

---
updated-dependencies:
- dependency-name: Optimization
  dependency-version: 4.0.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/Project.toml

@@ -28,6 +28,7 @@ DFTK = "0.7"
 Documenter = "~1.8, 1.16"
 EmpiricalPotentials = "0.2.5"
 GeometryOptimization = "0.1.5"
+Optimization = "4.0.0"
 PseudoPotentialData = "0.2"
 Unitful = "1.28.0"
 UnitfulAtomic = "1.0.0"