Update rstest requirement from 0.18 to 0.19 (#171)

Updates the requirements on [rstest](https://github.com/la10736/rstest) to permit the latest version.
- [Release notes](https://github.com/la10736/rstest/releases)
- [Changelog](https://github.com/la10736/rstest/blob/master/CHANGELOG.md)
- [Commits](la10736/rstest@v0.18.0...v0.19.0)

---
updated-dependencies:
- dependency-name: rstest
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Cargo.toml

@@ -18,7 +18,7 @@ rand = "0.8"
 biosphere = "0.3.0"
 
 [dev-dependencies]
-rstest = "0.18"
+rstest = "0.19"
 assert_approx_eq = "1.1"
 ndarray-rand = "0.14"
 ndarray = { version = "0.15", features = ["approx"] }