Standard license checks

[wlandau]

Fixes r-multiverse/help#158 and fixes tests.

[eitsupi]

This seems causing status check failure for many packages.

R-multiverse found issues with package polars version 0.22.4 remote hash 2b5b485fb178e47934c8041f03d4382f79a205f6 (last published at 2025-05-14 01:14:21.637 UTC).

Package polars declares license 'MIT + file LICENSE' in its DESCRIPTION file. R-multiverse cannot verify that this license is a [valid free and open-source license](https://en.wikipedia.org/wiki/Free_and_open-source_software). Each package contributed to R-multiverse must have a valid open-source license to protect the intellectual property rights of the package owners.


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