Lowercase for DOI

[eloiferrer]

Issue description:
We should save all DOIs in lowercase
We have now some double entries that need to be corrected, for instance https://portal.mardi4nfdi.de/wiki/Item:Q57679

TODOS:

• example todo to copy

Acceptance-Criteria

Checklist for this issue:

• Assignee has been set for this issue
• All fields of the issue have been filled
• Issue has been assigned to the main project
• Code was merged
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[eloiferrer]

This query provides the list of publications with more than 1 DOI, which are candidates to having repeated DOI: http://tinyurl.com/22huojf5

[eloiferrer]

I've just deleted the DOIs that were written in capital letters and kept only the lowercase version

[timconrad]

Sometime that actually have two DOIs: https://portal.mardi4nfdi.de/wiki/Item:Q71297

[LizzAlice]

TODO: in reference run, reupload zbmath dois as lowercase