#17650 ci(cmux-next): run OmnibarSelectionViewTests in the isolated field-editor step

Summary

OmnibarSelectionViewTests.aFocusingDragSelectsTheDraggedURL failed on #17601 (run 37509955149, attempt 3). The field showed the full URL with the caret at its end, {25, 0}, rather than the dragged {0, 19}.

This is the same failure #17626 found for OmnibarFieldEditorTests. In the shared test process, another UI suite moved the real field editor's state mid-test. In a 60-run census of recent cmux-next runs, every field-editor failure showed the same signature: a caret at the end of the full URL. OmnibarFieldEditorTests hit it in 3 jobs, and typed gi landed after https://example.org/start. No wait inside the test fixes it, because the field editor itself loses the state.

This change moves OmnibarSelectionViewTests into the isolated field-editor step next to OmnibarTypingTests and OmnibarFieldEditorTests, and skips it in the shared step. Every test still runs.

This PR is stacked on #17626 (it includes that branch). After #17626 lands, the diff is the one added suite.

Testing

• actionlint and python3 -m unittest tests.test_cmux_next_checks_workflow pass.
• This PR's cmux-next swift test job runs the suite in the isolated step.

Changelog

none

🤖 Generated with Claude Code

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Summary by cubic

Moves OmnibarSelectionViewTests and OmnibarFieldEditorTests into the isolated field-editor CI step and skips them in the shared step, so their drag-selection and IME tests no longer fail when another UI suite moves the field editor's state mid-test. Every test still runs.