missing temporary path to unpack testdata-minimal.tar.gz

[avaldebe]

This is likely an error on the underlying library (pooch).
There I create the temporary path before retrieving the test dataset.

close #996

[codecov]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (4ab7690) 78.94% compared to head (b022199) 78.93%.
Report is 66 commits behind head on main-dev.

Files	Patch %	Lines
pyaerocom/plugins/icos/reader.py	0.00%	8 Missing ⚠️
pyaerocom/geodesy.py	86.20%	4 Missing ⚠️
pyaerocom/aeroval/coldatatojson_engine.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           main-dev     #997      +/-   ##
============================================
- Coverage     78.94%   78.93%   -0.01%     
============================================
  Files           105      105              
  Lines         18421    18451      +30     
============================================
+ Hits          14543    14565      +22     
- Misses         3878     3886       +8     

Flag	Coverage Δ
unittests	78.93% <66.66%> (-0.01%)	⬇️

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[lewisblake]

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