Update table.ts

[k-manikandan]

I'm using Angular version 18.2 with material version 15.2.x. In this combination, I'm trying to render table using mat-table.

"tbody" or "thead" is not created in the DOM and throwing error in the edited line. Hence I'm checking whether the "tbody" is available or not before adding a class to it.

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[crisbeto]

Closing, because:

1. v18 is in LTS which means that we only merge fixes for severe issues into it.
2. Mixing Angular v18 and Material v15 isn't supported.

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