dev-cmd/pr-pull: require cask/cask_loader

[p-linnane]

brew pr-pull calls Cask::CaskLoader.load when working out which packages a pull request touches, but the file only required formula, so the constant was undefined and the command failed with a NameError on cask pull requests. This was reported in https://github.com/orgs/Homebrew/discussions/7034.

Requiring cask/cask_loader fixes it, and also covers the Cask::Cask references further down the file. This is the same class of missing require as the recent cmd/deps and cmd/uses fixes. The new spec loads dev-cmd/pr-pull in a fresh Ruby process so it actually catches the missing require instead of passing because another spec already loaded the cask code.

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Claude Code (Opus 5) drafted the implementation and tests; I reviewed the diff, verified the new test fails without the fix and passes with it, and ran brew lgtm + targeted specs.

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[Copilot]

Pull request overview

This pull request fixes a NameError in brew pr-pull for cask-related pull requests by ensuring the command file explicitly requires cask/cask_loader, so Cask::CaskLoader (and related cask constants used in the file) are always defined.

Changes:

• Add require "cask/cask_loader" to dev-cmd/pr-pull so cask-loading code paths work reliably.
• Add a regression spec that loads dev-cmd/pr-pull in a fresh Ruby process to catch missing requires that could be masked by prior test loads.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
Library/Homebrew/dev-cmd/pr-pull.rb	Requires cask/cask_loader so cask constants used by brew pr-pull are available.
Library/Homebrew/test/dev-cmd/pr-pull_spec.rb	Adds a subprocess-based regression test to ensure dev-cmd/pr-pull loads cask support independently.

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[MikeMcQuaid]

Thanks!