Fix Casida excitations output

Description

Put back the output of the Casida excitations. This was removed by mistake some time ago in !1111 (merged).

News snippet

Fixed Casida excitations output.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

changed milestone to %11.1

added Bugfix label

assigned to @nicolastd

approved this merge request

enabled an automatic merge when the pipeline for 6be3d2ed succeeds

unapproved this merge request

@micael.oliveira Should we add a warning saying that the output will not be produced in the distributed case?

approved this merge request

resolved all threads

mentioned in commit 5745f7da

merged