doc: Clarify version explanation of --json info

[okuramasafumi]

For formula, we don't have to specify v2.
This change makes it clear that we need to specify v2 only for cask. It now also explains how to specify version.

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brew lgtm failed, but it's not related to this change.

==> brew style --changed --fix
Library/Homebrew/cmd/info.rb:20:5: C: Style/Documentation: Missing top-level documentation comment for class Homebrew::Cmd::Info.
    class Info < AbstractCommand
    ^^^^^^^^^^
Library/Homebrew/cmd/info.rb:21:7: C: Style/Documentation: Missing top-level documentation comment for class Homebrew::Cmd::Info::NameSize.
      class NameSize < T::Struct
      ^^^^^^^^^^^^^^

1 file inspected, 2 offenses detected
Error: Failure while executing; `/opt/homebrew/bin/brew style --changed --fix` exited with 1.

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[Copilot]

Pull request overview

This PR updates the brew info command’s CLI help text to better explain the --json version behavior, especially distinguishing between formula and cask output.

Changes:

• Clarifies the --json flag description for brew info, emphasizing that --json=v2 is needed for casks while formula defaults to v1.

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[MikeMcQuaid]

Thanks!