MNT: Drop ciftilib back to 1.5, add bet2 as dep

Rebuilding melodic package against an updated ciftilib 1.5 recipe, where the ciftilib ABI compatibility constraint is enforced so that this melodic package will require ciftilib 1.5.* (see ciftilib!12 (merged) and https://git.fmrib.ox.ac.uk/fsl/conda/ciftilib/-/tree/maint/1.5.x).

melodic 2111.1 build 5 was never published (actually it was, but was then pulled from the channel), so the build number doesn't need to be bumped.

Closes #1 (closed)