Fix typing of schedules argument in Flow.to_deployment

[peterbygrave]

The current typing suggests input should be a list-of-list of schedules, but really should be a list of schedules. The 3 or 4 functions it passes it to expects Optional[FlexibleScheduleList].

Checklist

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[cicdw]

Good eye @peterbygrave , thank you!

[codspeed-hq]

CodSpeed Performance Report

Merging #14711 will not alter performance

_{Comparing peterbygrave:patch-1 (22f4222) with main (c5f1970)}

Summary

✅ 5 untouched benchmarks