[24.1] quota: do not complain on no-change of default

[bernt-matthias]

(and also no message)

Currently a quota update setting a non-default to non-default (i.e. doing nothing) raises a 400, e.g. on my instance

bioblend.ConnectionError: Unexpected HTTP status code: 400: {"err_msg":"Quota '[email protected]' is not a default.","err_code":400008}

xref: #18775

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  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

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