Fix json output error reporting

[Midnighter]

• [x] fix #603
• [x] description of feature/fix
• [x] tests added/passed
• [x] add an entry to the next release

[codecov[bot]]

Codecov Report

Merging #605 into develop will decrease coverage by 0.07%. The diff coverage is 12.5%.

@@             Coverage Diff             @@
##           develop     #605      +/-   ##
===========================================
- Coverage     79.8%   79.73%   -0.08%     
===========================================
  Files           59       59              
  Lines         3095     3099       +4     
  Branches       423      424       +1     
===========================================
+ Hits          2470     2471       +1     
- Misses         552      555       +3     
  Partials        73       73

Impacted Files	Coverage Δ
memote/suite/tests/test_thermodynamics.py	100% <ø> (ø)	:arrow_up:
memote/utils.py	74.15% <12.5%> (-2.32%)	:arrow_down:

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