requirements: update idna requirement from >=3.15 to >=3.18

[dependabot]

Updates the requirements on idna to permit the latest version.

Changelog

Sourced from idna's changelog.

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 any legitimate domain or label and guards against pathological inputs.

3.16 (2026-05-22)

• Add a command-line interface (python -m idna, also available as the idna script). Encodes or decodes one or more domains supplied as arguments or on standard input, with options to select A-label or U-label output and control error handling.
• Raise the minimum supported Python version to 3.9
• Various code quality improvements

3.15 (2026-05-12)

• Enforce DNS-length cap on individual labels early in check_label, short-circuiting contextual-rule processing for oversized input while staying compatible with UTS 46 usage.
• Tidy core helpers: hoist bidi category sets to module-level frozensets (avoiding per-codepoint list construction), simplify length checks, and reuse the shared _unicode_dots_re from idna.core in the codec module.
• Use raise ... from err for proper exception chaining and switch internal string formatting to f-strings.
• Allow flit_core 4.x in the build backend.
• Expand the ruff lint set (flake8-bugbear, flake8-simplify, pyupgrade, perflint) and apply the surfaced fixes; pin lint CI to Python 3.14.
• Add Dependabot configuration for GitHub Actions.
• Convert README and HISTORY from reStructuredText to Markdown.
• Reference CVE-2026-45409 for the 3.14 advisory in place of the initial GHSA identifier.

Thanks to Felix Yan, Stan Ulbrych, and metsw24-max for contributions to this release.

3.14 (2026-05-10)

• Removed opportunity to process long inputs into quadratic time by rejecting oversize inputs up-front. Closes a bypass

... (truncated)

Commits

• f39ea90 Release 3.18
• 40f4e40 Pre-release 3.18rc0
• 1a5bf80 Merge pull request #253 from kjd/lenient-decode
• 5bbb26f Merge branch 'master' into lenient-decode
• c532bae Rename decode() lenient= option to display= (issue #248)
• 0b1758b Merge pull request #252 from kjd/release-3.17
• f48619c Release 3.17
• 7421ba8 Pre-release 3.17rc0
• 22ebb73 Merge pull request #251 from kjd/structure-optimizations
• 2a7ac0a Drop redundant parallel-arrays comment from uts46data
• Additional commits viewable in compare view

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