Reduce test warnings

[thorbjoernl]

Change Summary

Fixes issues that lead to the following warnings:

• ResourceWarning due to a unclosed file handle.
• DeprecationWarning due to not indexing 1d array before converting to scalar.

After these changes the only warnings remaining are the matplotlib related ones, and the iris default sphere ones we decided to ignore in #1394

Related issue number

#1066 (Remember to push this forward two milestones when merging)

Checklist

• Start with a draft-PR
• The PR title is a good summary of the changes
• PR is set to AeroTools and a tentative milestone
• Documentation reflects the changes where applicable
• Tests for the changes exist where applicable
• Tests pass locally (except Issue with test pytest tests/io/test_read_aeronet_invv3.py #1455 )
• Tests pass on CI
• At least 1 reviewer is selected
• Make PR ready to review

[codecov]

Codecov Report

Attention: Patch coverage is 78.72340% with 10 lines in your changes missing coverage. Please review.

Project coverage is 78.43%. Comparing base (239efbc) to head (11c11fb).
Report is 8 commits behind head on main-dev.

Files with missing lines	Patch %	Lines
pyaerocom/io/ebas_nasa_ames.py	77.27%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           main-dev    #1456   +/-   ##
=========================================
  Coverage     78.43%   78.43%           
=========================================
  Files           137      137           
  Lines         20961    20963    +2     
=========================================
+ Hits          16440    16442    +2     
  Misses         4521     4521           

Flag	Coverage Δ
unittests	78.43% <78.72%> (+<0.01%)	⬆️

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[heikoklein]

Thanks, looks very good.