CI should check that base beets specifies it dependencies completely

[wisp3rwind]

See the discussion in #5695: We might want to run CI without any extras activated to verify that also in that case, all dependencies are pulled in.

[semohr]

Additionally, we could move the typing_extensions into the main dependencies. I don't see why this would be a bad choice either.

There might be some future python typing features we want to use in the codebase without moving the minimal python requirement. E.g. using ReadOnly would require python 3.13 without typing extensions. At the moment we could not use this feature at all, as typing_extensions would be required for python > 3.10 which we are not installing as it is an extra.

Also typing_extensions is most likely the only dependency that is pulled in via some extras, which shouldn't be installed.