Fix compilation of Evoformer (#7862)
`EvoformerAttnBuilder` returns instances of `Path` from `include_paths`
which then cause failures in `OpBuilder.builder` when passing them to
`strip_empty_entries` that calls `len` on them which isn't defined for
`Path` instances:
> TypeError: object of type 'PosixPath' has no len()
Fixes regression introduced in #7760
cc @sdvillal
Signed-off-by: Alexander Grund <alexander.grund@tu-dresden.de>
