chore: add changelog entry for Homebrew postflight fix

[kyletruong]

Summary

Adds a ### Fixed entry under ## Unreleased for #97, which moved the Homebrew cask from the deprecated postflight stanza to postflight_steps. Without that change, every brew command that loads xdevplatform/tap/xurl prints a "Calling postflight is deprecated" warning.

The Cut Release workflow refuses to run when ## Unreleased has no bullet entries, so this gives the v1.3.2 release something to promote without needing skip_changelog.

After merge

Run Actions → Cut Release from main with bump=patch and both checkboxes unchecked. That publishes v1.3.2 and regenerates the Homebrew cask with postflight_steps.

Test plan

• python3 scripts/cut_release.py --bump patch --dry-run resolves v1.3.2 and moves this entry under ## v1.3.2.
• After the release, brew update && brew upgrade xurl no longer prints the deprecation warning and xurl still runs.

[CLAassistant]

All committers have signed the CLA.