Update polars requirement from <1.20 to <1.21

Updates the requirements on [polars](https://github.com/pola-rs/polars) to permit the latest version.
- [Release notes](https://github.com/pola-rs/polars/releases)
- [Commits](pola-rs/polars@py-0.0.1...py-1.20.0)

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

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

Author: dependabot[bot]

pyproject.toml

@@ -109,7 +109,7 @@ optional-dependencies.all = [
 ]
 optional-dependencies.cfr = [
   "pandas<2.3",
-  "polars<1.20",
+  "polars<1.21",
   "pyarrow<18.2",
 ]
 optional-dependencies.cloud = [
@@ -152,7 +152,7 @@ optional-dependencies.io = [
   "dask[dataframe]>=2020",
   "fsspec[s3,http]",
   "pandas>=1,<2.3",
-  "polars<1.20",
+  "polars<1.21",
   "sqlalchemy>=2",
   "universal-pathlib<0.3",
 ]