[BUG]: boken use of CF conventions for Level4

[d70-t]

In JOANNE Level4 data as found in the EUREC4A intake catalog,
circle is marked as

	int64 circle(circle) ;
		circle:standard_name = "time" ;
		circle:long_name = "circle number" ;
		circle:units = "" ;

i.e. standard_name is "time", but the variable actually contains the circle number (i.e. not a time). In contrast, circle_time is marked as:

	double circle_time(circle) ;
		circle_time:_FillValue = NaN ;
		circle_time:long_name = "mean launch time of all sondes in circle" ;
		circle_time:axis = "T" ;
		circle_time:units = "seconds since 2020-01-01" ;
		circle_time:calendar = "proleptic_gregorian" ;

i.e. it actually contains a time, but this isn't reflected by the standard_name attribute.

The error occured to me as I wanted to automatically collect the time ranges of multiple datasets using CF-Conventions, but this didn't work out with this dataset.