if-guards in Thing cannot work

i just stumbled over some buggy implementation of thing..

we've multiple lines like if "some" and "other" in a_dict.keys(): like for example in https://git.ufz.de/rdm-software/timeseries-management/tsm-dispatcher/-/blob/main/src/thing.py#L36

Unfortunately this does not work as expected, because each string will act as a own condition and therfore only the last string will be checked if it is present in keys().