Parallelize upload_mock integration tests

[cmaglie]

Please check if the PR fulfills these requirements

See how to contribute

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• The PR follows
  our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)
• configuration.schema.json updated if new parameters are added.

What kind of change does this PR introduce?

Parallelize upload_mock integration test.
Since the upload_mock tests are the longest, this change should reduce the overall execution time, I didn't check accurately, but I'm pretty sure we are gaining at least a couple of minutes over the full CI process.

What is the current behavior?

test-integration (windows-latest, upload_modk) completes in roughly ~12 minutes.

What is the new behavior?

test-integration (windows-latest, upload_modk) completes in roughly ~8 minutes.

Does this PR introduce a breaking change, and is titled accordingly?

Other information

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ab03161) 67.38% compared to head (a41a88a) 67.32%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2444      +/-   ##
==========================================
- Coverage   67.38%   67.32%   -0.07%     
==========================================
  Files         210      210              
  Lines       20591    20591              
==========================================
- Hits        13876    13862      -14     
- Misses       5578     5588      +10     
- Partials     1137     1141       +4     

Flag	Coverage Δ
unit	67.32% <ø> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.