Apply lowering when cleaning Publication fields

[chrisvanrun]

A minor issue popped up: validation on the form field did not do a lower() on the identifier, meaning if any cases made it to the publication (i.e. "10.1016/S1470-2045(24)00220-1") it would not validate.

It does seem that a DOI with case 'S' should be allowed, and since 's' and 'S' are to be matched for duplication detection I've opted to clean the field rather than change the regex.