Revert "Revert "Revert "[CMake] Bumps minimum version to 3.20.0."""

This reverts commit 1ef4c3c859728008cf707cad8d67f45ae5070ae1.

Two buildbots still haven't been updated.

GitOrigin-RevId: 44d38022ab29a3156349602733b3459df5beef93
1 file changed