Brew: 4.5.6 Release

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

This release contains preliminary macOS 26 Tahoe support. When using macOS 26 betas, remember that: * You must also update Xcode and the CLT to 26.0 beta * brew install will default to Sequoia bottles until closer to release, so formulae like pkg-config, gcc and llvm will use the macOS 15 SDK when installed from a bottle and may not work correctly * Formulae built from source may or may not work depending on whether upstreams support macOS/Xcode 26 yet

What's Changed

• Preliminary macOS 26 (Tahoe) support by @Bo98 in https://github.com/Homebrew/brew/pull/20062
• cmd/vendor-install: fix exit code handling for curl by @Bo98 in https://github.com/Homebrew/brew/pull/20063
• Reduce Homebrew/brew CI warnings by @MikeMcQuaid in https://github.com/Homebrew/brew/pull/20054
• workflows/tests.yml: more CI tweaks. by @MikeMcQuaid in https://github.com/Homebrew/brew/pull/20060
• Cleanup extend/ directory usage. by @MikeMcQuaid in https://github.com/Homebrew/brew/pull/20061

Full Changelog: https://github.com/Homebrew/brew/compare/4.5.5...4.5.6