ci: use code-gen 1.20
ci: use code-gen 1.20

Let's just the same version as our go.mod suggests. This workaround
seems old and not necessary anymore.

Signed-off-by: Sébastien Han <62d754cc350e84d3b1c32ae79f976f5348e74a40@redhat.com>

rook/rook,rook/nfs,rook/rook,rook/nfs,rook/rook,rook/rook,rook/rook,rook/nfs