Brew: 4.4.21 Release

<!-- Release notes generated using configuration in .github/release.yml at master -->

What's Changed

• docker: fix comment for ubuntu 18 deprecation by @iMichka in https://github.com/Homebrew/brew/pull/19190
• Add rebottling documentation in BrewTestBot-For-Maintainers.md by @Moisan in https://github.com/Homebrew/brew/pull/19212
• Add arm64 Linux build for Portable Ruby by @Bo98 in https://github.com/Homebrew/brew/pull/19224
• github_packages: fix oldest CPU variant on arm64 Linux by @Bo98 in https://github.com/Homebrew/brew/pull/19223
• dev-cmd/pr-upload: allow --keep-old with --upload-only by @Bo98 in https://github.com/Homebrew/brew/pull/19222
• ci: switch to SSH signing everywhere by @woodruffw in https://github.com/Homebrew/brew/pull/19230
• dev-cmd: add brew verify by @woodruffw in https://github.com/Homebrew/brew/pull/19217
• Split up SoftwareSpec by @MikeMcQuaid in https://github.com/Homebrew/brew/pull/19234
• tests: add missing :needs_network argument by @samford in https://github.com/Homebrew/brew/pull/19239
• formula_creator: depend on latest python by @gromgit in https://github.com/Homebrew/brew/pull/19244
• docs: various manpage grammar fixes by @EricFromCanada in https://github.com/Homebrew/brew/pull/19220
• Add test for concurrent fetching by @dduugg in https://github.com/Homebrew/brew/pull/19215
• glibc: set next version by @iMichka in https://github.com/Homebrew/brew/pull/19238
• utils/pypi: warn when pypi_info fails due to missing sources by @woodruffw in https://github.com/Homebrew/brew/pull/19250
• update-python-resources: add option to ignore errors by @gromgit in https://github.com/Homebrew/brew/pull/19252
• Revert json v3 logic by @apainintheneck in https://github.com/Homebrew/brew/pull/19251
• brew.sh: improve HOMEBREW_FORCE_BREW_WRAPPER error message by @MikeMcQuaid in https://github.com/Homebrew/brew/pull/19257
• livecheck: Add support for POST requests by @samford in https://github.com/Homebrew/brew/pull/19233
• Import brew alias and brew unalias commands by @MikeMcQuaid in https://github.com/Homebrew/brew/pull/19258
• Enforce that all docs have last_review_date frontmatter by @issyl0 in https://github.com/Homebrew/brew/pull/19264
• Review some docs by @issyl0 in https://github.com/Homebrew/brew/pull/19265
• utils/pypi: remove extra newline when updating resources by @branchvincent in https://github.com/Homebrew/brew/pull/19266
• Import brew formula-analytics and generate-analytics-api commands by @MikeMcQuaid in https://github.com/Homebrew/brew/pull/19259
• workflows/docker: continue to deploy master images by @ZhongRuoyu in https://github.com/Homebrew/brew/pull/19274
• Fix "can't modify frozen String" error by @ArtRoman in https://github.com/Homebrew/brew/pull/19276
• Refactor Livecheck::Strategy to remove module_function use by @dduugg in https://github.com/Homebrew/brew/pull/19278
• More Sorbet typed: strict RuboCops by @issyl0 in https://github.com/Homebrew/brew/pull/19195
• rubocops/lines: Clean up an old TODO by @issyl0 in https://github.com/Homebrew/brew/pull/19277
• Use delegation to create Cask DSL methods by @dduugg in https://github.com/Homebrew/brew/pull/19288
• clear core tap cache on formula creation by @gromgit in https://github.com/Homebrew/brew/pull/19283
• docs/Homebrew-Governance.md: fix broken link by @bevanjkay in https://github.com/Homebrew/brew/pull/19298
• Clean up OnSystem rbis by @dduugg in https://github.com/Homebrew/brew/pull/19306
• cmd/info: only display keg info if tap matches by @ZhongRuoyu in https://github.com/Homebrew/brew/pull/19295
• cask/url: remove arch placeholder when checking if unversioned by @zyoshoka in https://github.com/Homebrew/brew/pull/19284

New Contributors

• @ArtRoman made their first contribution in https://github.com/Homebrew/brew/pull/19276

Full Changelog: https://github.com/Homebrew/brew/compare/4.4.20...4.4.21