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

Unfortunatly not all buildbots are updated.

This reverts commit ffb807ab5375b3f78df198dc5d4302b3b552242f.

GitOrigin-RevId: e8e8707b4aa6e4cc04c0cffb2de01d2de71165fc
1 file changed