Group on_system_conditional after os

[AlternateRT]

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Needed before merging:

• various: group/order missing stanzas, part 1 homebrew-cask#277510
• various: group/order missing stanzas, part 2 homebrew-cask#277547
• various: group/order missing stanzas, part 3 homebrew-cask#277548
• various: group/order missing stanzas, part 4 homebrew-cask#277549
• various: group/order missing stanzas, part 5 homebrew-cask#277550
• Add missing on_<system> stanzas to cask stanza order #23321

Temporarely disables missing_line_after? check for os stanza. Will be reverted in #23321.

[MikeMcQuaid]

Thanks!