Update Flux requirement from 0.14.21 to 0.14.21, 0.16

Updates the requirements on [Flux](https://github.com/FluxML/Flux.jl) to permit the latest version.
- [Release notes](https://github.com/FluxML/Flux.jl/releases)
- [Changelog](https://github.com/FluxML/Flux.jl/blob/master/NEWS.md)
- [Commits](FluxML/Flux.jl@v0.14.21...v0.16.9)

---
updated-dependencies:
- dependency-name: Flux
  dependency-version: 0.16.9
  dependency-type: direct:production
...

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

Author: dependabot[bot]

Project.toml

@@ -23,7 +23,7 @@ ChainRules = "1.72.6"
 ChainRulesCore = "1.25.2"
 DiffOpt = "0.5.4"
 FillArrays = "1.14.0"
-Flux = "0.14.21"
+Flux = "0.14.21, 0.16"
 JLD2 = "0.6.3"
 JuMP = "1.29.4"
 MathOptInterface = "1.48.0"