Bump polars from 0.17.7 to 0.20.8

Bumps [polars](https://github.com/pola-rs/polars) from 0.17.7 to 0.20.8.
- [Release notes](https://github.com/pola-rs/polars/releases)
- [Commits](pola-rs/polars@py-0.17.7...py-0.20.8)

---
updated-dependencies:
- dependency-name: polars
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

poetry.lock

@@ -41,7 +41,7 @@ pytest-mock = "^3.10.0"
 # for datatype testing
 Faker = ">=15.3.4,<19.0.0"
 geopandas = "^0.12.2"
-polars = ">=0.16.12,<0.18.0"
+polars = ">=0.16.12,<0.21.0"
 modin = { extras = ["all"], version = "^0.19.0" }
 dask = "^2023.3.1"
 vaex = "^4.16.0"