CI: test optional datasets on every commit

[adamjstewart]

TorchGeo has a number of optional dependencies only needed by certain datasets. Until now, we've only ensured that all tests pass without these dependencies installed on release branches. However, this makes it difficult to get full coverage without relying on ugly import monkeypatching. It's simpler and easier to test both on every commit to get full coverage. We already do this for the minimum version of our dependencies.

Prerequisite for #2043