Update polars requirement from <1.20 to <1.21

[dependabot]

Updates the requirements on polars to permit the latest version.

Release notes

Sourced from polars's releases.

Python Polars 1.20.0

⚠️ Deprecations

• Make parameter of str.to_decimal keyword-only (#20570)

🚀 Performance improvements

• Extend functionality on BitmapBuilder and use in Growables (#20754)
• Specialize first/last agg for simple types in new-streaming engine (#20728)
• Use PyO3 to convert between Python and Rust datetimes (#20660)
• Improve state caching and parallelism of window functions (#20689)
• Broadcast without materialization in concat_arr (#20681)
• Cache rolling groups (#20675)
• Use downcast_ref instead of dtype equality in <dyn SeriesTrait as AsRef<ChunkedArray<T>> (#20664)
• Fix performance regression for DataFrame serialization/pickling (#20641)
• Make Parquet verify_dict_indices SIMD (#20623)
• Move to zlib-rs by default and use zstd::with_buffer (#20614)
• Skip filter expansion in eager (#20586)
• Improve unique pred-pd (#20569)

✨ Enhancements

• Allow different python versions for pickle (#20740)
• Add SQL support for the NORMALIZE string function (#20705)
• Add 'allow_exact_matches' join_asof' (#20723)
• Add new-streaming first/last aggregations (#20716)
• Add Parquet Sink to new streaming engine (#20690)
• Make automatic use of Azure storage account keys opt-in (#20652)
• Reduce scan_csv() (and friends') memory usage when using BytesIO (#20649)
• Improve GroupsProxy/GroupsPosition to be sliceable and cheaply cloneable (#20673)
• Add str.normalize() (#20483)
• Allow more group_by agg expressions in the new streaming engine (#20663)
• Support loading Excel Table objects by name (#20654)
• Support writing to file objects from write_excel (#20638)
• Raise DuplicateError if given a pyarrow Table object with duplicate column names (#20624)
• Support writing partitioned parquet to cloud (#20590)
• Add hint to error message for extra struct field in JSON (#20612)
• Add index_of() function to Series and Expr (#19894)
• Update sqlparser-rs, enabling "LEFT" keyword to be optional for anti/semi joins in SQL queries (#20576)
• Add cat.starts_with/cat.ends_with (#20257)

🐞 Bug fixes

• Avoid blocking on async runtime when resolving cloud scans (#20750)
• Fix allow_invalid_certificates being ignored in storage_options (#20744)
• Incorrect output type for map_groups returning all-NULL column (#20743)
• Fix unique(maintain_order=True) raising InvalidOperationError for null array (#20737)
• Don't collapse into a Nested Loop Join if the cross join maintains order (#20729)
• Don't serialize credentials provider (#20741)
• Fix Series.n_unique raising for list of struct (#20724)

... (truncated)

Commits

• 725c960 perf: Extend functionality on BitmapBuilder and use in Growables (#20754)
• acb20ee chore: Fix remote benchmark script (#20755)
• 6ce00e1 docs(python): Add more information for cross joins (#20753)
• 54fc488 Python Polars 1.20.0 (#20752)
• 28a45f2 refactor: Fix flaky test (#20751)
• cf4b9bd fix: Avoid blocking on async runtime when resolving cloud scans (#20750)
• ce9ad17 fix: Fix allow_invalid_certificates being ignored in storage_options (#20...
• 68f547e fix: Incorrect output type for map_groups returning all-NULL column (#20743)
• 233b396 fix: Fix unique(maintain_order=True) raising InvalidOperationError for nu...
• f56affc test: Fix tests (#20745)
• Additional commits viewable in compare view

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot merge will merge this PR after your CI passes on it
• @dependabot squash and merge will squash and merge this PR after your CI passes on it
• @dependabot cancel merge will cancel a previously requested merge and block automerging
• @dependabot reopen will reopen this PR if it is closed
• @dependabot close will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually
• @dependabot show <dependency name> ignore conditions will show all of the ignore conditions of the specified dependency
• @dependabot ignore this major version will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this minor version will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)

[amotl]

@dependabot rebase