Update OrderedCollections requirement to 1.8.1 (#34)

Updates the requirements on [OrderedCollections](https://github.com/JuliaCollections/OrderedCollections.jl) to permit the latest version.
- [Release notes](https://github.com/JuliaCollections/OrderedCollections.jl/releases)
- [Commits](JuliaCollections/OrderedCollections.jl@v0.1.0...v1.8.1)

---
updated-dependencies:
- dependency-name: OrderedCollections
  dependency-version: 1.8.1
  dependency-type: direct:production
...

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Project.toml

@@ -21,6 +21,7 @@ ForwardDiff = "1"
 JuMP = "1.29.4"
 MathOptInterface = "1.40"
 NaNMath = "1"
+OrderedCollections = "1.8.1"
 SparseArrays = "1.10"
 SpecialFunctions = "2.6.1"
 julia = "1.10"