Adjust Subversion checkout operands

[MikeMcQuaid]

• Keep svn checkout option parsing separate from repository operands.
• Cover the multi-revision checkout path to preserve that ordering.

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[Copilot]

Pull request overview

This pull request adjusts how svn checkout arguments are constructed in SubversionDownloadStrategy to ensure option parsing stays separate from repository operands, and adds a regression test that exercises the multi-revision checkout path (including externals) to preserve the intended ordering.

Changes:

• Reorder svn checkout arguments to place options first and terminate option parsing with -- before the URL and target.
• Add a spec covering :revisions (trunk + externals) to assert checkout operands remain after options, including when an external URL could be interpreted as an option.

Reviewed changes

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

File	Description
Library/Homebrew/download_strategy/subversion_download_strategy.rb	Moves svn checkout to ["checkout", *options, "--", url, target] to prevent operands being misparsed as options (or vice versa).
Library/Homebrew/test/download_strategies/subversion_spec.rb	Adds coverage for :revisions checkout to lock in the corrected operand/option ordering for trunk and externals.

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