Fix missing close-parens for In filter's toString

Otherwise the open parentheses isn't closed in query plan descriptions of batch scans.

    PushedFilters: [In(COL_A, [1,2,4,6,10,16,219,815], IsNotNull(COL_B), ...

Author: Andrew Ash <andrew@andrewash.com>

Closes #16558 from ash211/patch-9.