build(deps): Update idna requirement from >=3.19 to >=3.20

[dependabot]

Updates the requirements on idna to permit the latest version.

Release notes

Sourced from idna's releases.

v3.20

• Update to Unicode 18.0.0.
• Better enforcement of the domain length limit in the incremental codec.
• Add support for Python 3.15.

Changelog

Sourced from idna's changelog.

3.20 (2026-09-17)

• Update to Unicode 18.0.0.
• Better enforcement of the domain length limit in the incremental codec.
• Add support for Python 3.15.

3.19 (2026-08-18)

• Restore the std3_rules option, which had no effect since changes to UTS #46 processing in Unicode 16. Note that uts46_remap() defaults to enabling STD3 rules, so direct callers will see input containing non-LDH ASCII characters rejected again.
• Performance improvements to UTS #46 mapping, particularly for ASCII-only domains.
• Test on free-threaded CPython with the GIL disabled and document thread safety.
• Expose the Unicode version of the generated tables as idna.unicode_version, and show it in idna --version.
• Add code, text, codepoint and position attributes to IDNAError so that the failed rule and the offending character can be identified without parsing the exception message.
• The deprecated transitional argument to encode() and uts46_remap() is now completely ignored, and gives a deprecation warning for the latter.
• Reject A-labels that are not the canonical Punycode encoding of their U-label.
• Fix CONTEXTJ violations raising IDNAError instead of InvalidCodepointContext.
• Consistently raise IDNAError for empty labels and non-ASCII bytes passed to label helper functions and the incremental codec.
• Add property-based tests, extended fuzzing targets, coverage measurement, and CI checks that the data tables match the generator output.
• Various code quality and tooling improvements.

Thanks to stefan6419846, LouieLuNZ, and Salvatore Corvaglia for contributions to this release.

3.18 (2026-06-02)

• When decoding a domain, add a display argument that will pass through invalid labels rather than raising an exception.

3.17 (2026-05-28)

• Substantial 75% reduction in memory usage through new data structures and some optimization in processing speed.
• Added a general 1024-character input length cap to the public validation, conversion, and codec entry points. This is well above

... (truncated)

Commits

• d55e65e Release 3.20
• 0c0824a Pre-release 3.20rc0
• bd7c316 Note Python 3.15 support in the 3.20 changelog
• b6cce85 Merge pull request #276 from kjd/unicode-18
• 9a4bc59 Update to Unicode 18.0.0
• dfab5a0 Merge branch 'python-3.15'
• 417c354 Read the latest Unicode version from the DerivedAge.txt header instead of the...
• cd17392 Merge pull request #274 from kjd/fix-decode-length-check
• c5796d7 Skip the decode round-trip check for domains past encode's length limit
• d6ee690 Update to Python 3.15 release candidate in CI and add trove classifier
• Additional commits viewable in compare view

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