tap-new: use run_as_real_uid: instead of Utils::UID.drop_euid

[carlocab]

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Now that SystemCommand supports run_as_real_uid:, replace the
Utils::UID.drop_euid block in tap-new with system_command! calls
using run_as_real_uid: true, and remove the now-unused drop_euid method.

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

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As seen above, I used Claude to generate this PR. I reviewed the diff and ran brew lgtm manually.

This is a follow-up to #21838. We should remove Utils::UID.drop_euid because it is prone to race conditions.

[Copilot]

Pull request overview

This PR updates brew tap-new to avoid process-wide EUID switching by using SystemCommand’s run_as_real_uid: option for the git operations that should run as the real UID, and removes the now-unused Utils::UID.drop_euid helper.

Changes:

• Replace the Utils::UID.drop_euid block in tap-new with system_command! calls using run_as_real_uid: true.
• Add SystemCommand::Mixin usage to tap-new to support the new command invocation.
• Remove Utils::UID.drop_euid from utils/uid.rb now that it has no callers.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Library/Homebrew/utils/uid.rb	Removes the drop_euid helper now that callers have migrated away from process-wide EUID changes.
Library/Homebrew/dev-cmd/tap-new.rb	Runs git commands via system_command! with run_as_real_uid: true to avoid EUID race conditions.

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[MikeMcQuaid]

Makes sense!