revert eigensolver change
Description
The change of the eigensolver in the attempt to make test shorter revealed a problem. As this MR is not related to that part of the code, we reverted the eigensolver back to rmmdiis.
News snippet
Revert changes to a test.
Checklist
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I have checked that my code follows the Octopus coding standards -
I have added tests for all the new features added in this request.
Edited by Martin Lueders