Some keyservers, e.g. keyserver.ubuntu.com (Hockeypuck), do not provide the key fingerprints by default. By setting the fingerprint variable to on in the request URL, we can explicitly ask HKP keyservers to provide the fingerprints when listing keys.
Note that Kleopatra does not work properly without fingerprints (see T5725: Kleopatra: Certificate lookup shows only one result even if there are 100s matches). Arguably, that needs to be fixed in Kleopatra, but dirmngr should still ask for the fingerprints.