Simon Cowell has had to pull out of Britain's Got Talent filming because he is still recovering from spinal surgery. The 66-year-old media mogul broke his back in an electric bike accident in 2020 and has undergone multiple operations since then, most recently a "routine" procedure last month. And while he recovers from the operation, Amanda Holden, Alesha Dixon and KSI will be joined by a guest judge during the Blackpool auditions for the talent show, though production company Fremantle are planning to postpone around half of the six-day schedule to January so Simon can still be involved as head judge. A source told The Sun on Sunday…