Is it permissible to dispose of music CDs by donating them to a charity shop or to others without charge, knowing that they contain forbidden things?

You must remove the music from the discs and reuse them by copying beneficial material onto them, or by giving them to a charitable organization that can do so. If copying is not possible, then they must be destroyed. It is not permissible to sell or donate them to any person or entity for listening, as that would constitute cooperation in sin.