Update DataFrames requirement to 1.8.1 in /docs

Updates the requirements on [DataFrames](https://github.com/JuliaData/DataFrames.jl) to permit the latest version.
- [Release notes](https://github.com/JuliaData/DataFrames.jl/releases)
- [Changelog](https://github.com/JuliaData/DataFrames.jl/blob/main/NEWS.md)
- [Commits](JuliaData/DataFrames.jl@v0.0.0...v1.8.1)

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

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

Author: dependabot[bot]

docs/Project.toml

@@ -14,6 +14,7 @@ Suppressor = "fd094767-a336-5f1f-9728-57cf17d0bbfb"
 
 [compat]
 CodecXz = "0.7.4"
+DataFrames = "1.8.1"
 Documenter = "1.16.1"
 Latexify = "0.16.10"
 Plots = "1.41.3"