pythonPackages.pycaption: fix build (#46356)

The `beaitufulsoup4` package distributed by `nixpkgs` is now at `4.6.3`.

Additionally it fixes `gnomecaption` which depends on the broken
`pycaption` package.

See https://hydra.nixos.org/build/81000247
See https://hydra.nixos.org/build/80723223

Addresses #45960