Generatemde single quotes replaced by double for json

[mpatrou]

Short description of the changes:

singlee quotes in values for json.loads in Generatemde were replaces with double quotes.
test added

Long description of the changes:

Check list for the pull request

• I have read the [CONTRIBUTING]
• I have read the [CODE_OF_CONDUCT]
• I have added tests for my changes
• I have updated the documentation accordingly

Check list for the reviewer

• I have read the [CONTRIBUTING]
• I have verified the proposed changes
• best software practices
  • all internal functions have an underbar, as is python standard
  • clearly named variables (better to be verbose in variable names)
  • code comments explaining the intent of code blocks
• All the tests are passing
• The documentation is up to date
• code comments added when explaining intent

Manual test for the reviewer

References

[Shiver] Json double quotes in generate mde

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 82.33%. Comparing base (b4a8b69) to head (4d40278).
Report is 1 commits behind head on next.

Files with missing lines	Patch %	Lines
src/shiver/models/generate_dgs_mde.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             next     #151   +/-   ##
=======================================
  Coverage   82.33%   82.33%           
=======================================
  Files          39       39           
  Lines        6209     6209           
=======================================
  Hits         5112     5112           
  Misses       1097     1097           

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