Add grouped_rolling test with STRUCT groupby keys.

[mythrocks]

Fixes #8887.

#9024 added support for STRUCT groupby keys.
This commit adds a test for grouped_rolling_window() where the groupby keys are STRUCT.

[codecov]

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[mythrocks]

@gpucibot merge

[mythrocks]

Thanks for the reviews, chaps. I've merged this now.