[@mantine.core] fix SegmentedControl rerender indicator when data len…

[Han5991]

🔧 Summary

Fixes an issue where the FloatingIndicator in SegmentedControl does not re-render when the data prop changes in length.

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🐞 Problem

Previously, the useShallowEffect responsible for triggering re-renders was dependent on the data array reference:

useShallowEffect(() => {
  setKey(randomId());
}, [data]);

✅ Fix

useShallowEffect(() => {
 setKey(randomId());
}, [data.length]);

This ensures proper re-rendering when the number of segments changes.

📎 Context

This change is especially helpful in cases where the data array is dynamically built (e.g. from user input or async responses), and the reference remains stable despite changes in content.

Fixes #7717

[rtivital]

Thanks!