Fix downloading diagnostics more than once

[TheJulianJES]

Proposed change

This PR makes a deepcopy of the device's original_signature before modifying the it for a friendlier version in the JSON.
Otherwise, we modify the original device.original_signature and fail with the error below when trying to download diagnostics for the same device a second time.

This fixes the following error when downloading diagnostics:

ep["profile_id"] = f"0x{ep['profile_id']:04x}"                                                                                                                                                                                                                                            
                           ^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                                                                                                             
ValueError: Unknown format code 'x' for object of type 'str'

Additional information

We can also test the diagnostics stay the same for every device, but that seems a bit overkill: 6d3c660 (this PR)
Now, the PR only tests it for one device (which has an original_signature). The test is in test_discover.py, which isn't great, but just creating test_diagnostics.py for this seems a bit overkill? But I can do that, of course.
It's under the existing diagnostics usage in test_discover.py for now.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.41%. Comparing base (558bc6f) to head (7c369c6).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #661   +/-   ##
=======================================
  Coverage   97.41%   97.41%           
=======================================
  Files          62       62           
  Lines       10724    10725    +1     
=======================================
+ Hits        10447    10448    +1     
  Misses        277      277           

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.