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

The owner of the last two failing buildbots updated CMake.

This reverts commit e8e8707b4aa6e4cc04c0cffb2de01d2de71165fc.

GitOrigin-RevId: 65429b9af6a2c99d340ab2dcddd41dab201f399c
1 file changed