Pass props as strings to avoid validation errors.

[rtibbles]

Summary

• Passes span prop as a string to validate for KDS component

References

Fixes #8810

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[sairina]

lgtm!

[indirectlylit]

KFixedGridItem allows a number for span, so a better fix would be to update CategorySearchModalOptions

https://design-system.learningequality.org/kfixedgriditem/#prop:span

[rtibbles]

Updated accordingly - I thought I had seen issues with KFixedGridItem parsing Numbers, but it may have just been exactly this context previously.