fix: CI should not rely on external resources / CI CodeCov upload workaround

[cmaglie]

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• 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?

• The CI was failing for a resource being denied on the CI runners. The integration tests run normally on my local PC I suspect the download has been blocked specifically from the GitHub runner IPs, or maybe it hit some rate limiting.
• CodeCov uploader has a bug that prevents uploading coverage if there is a broken link in the repo. I've created a workaround until the bug is fixed: [BUG] REGRESSION: v5 fails if a broken symlink is present in the repo codecov/codecov-action#1890

What is the current behavior?

• Arduino CLI integration test CI fails with:

Retrokits-RK002:[email protected] 0 B / ?    0.00%
Retrokits-RK002:[email protected] Server responded with: 403 Forbidden
Error during install: Server responded with: 403 Forbidden
ESC[90m<<< Run completed (err = exit status 1)ESC[0m
    core_test.go:832:
           Error Trace:    /home/runner/work/arduino-cli/arduino-cli/internal/integrationtest/core/core_test.go:832
           Error:          Received unexpected error:
                           exit status 1
           Test:           TestCoreListSortedResults
--- FAIL: TestCoreListSortedResults (3.76s)

• CodeCov uploader fails with this error:

Traceback (most recent call last):
  File "codecov_cli/main.py", line 100, in <module>
  File "codecov_cli/main.py", line 96, in run
  File "click/core.py", line 1161, in __call__
  File "click/core.py", line 1082, in main
  File "click/core.py", line 1697, in invoke
  File "click/core.py", line 1443, in invoke
  File "click/core.py", line 788, in invoke
  File "click/decorators.py", line 33, in new_func
  File "codecov_cli/commands/upload_coverage.py", line 86, in upload_coverage
  File "click/core.py", line 788, in invoke
  File "codecov_cli/services/upload_coverage/__init__.py", line 52, in upload_coverage_logic
  File "codecov_cli/services/upload/__init__.py", line 104, in do_upload_logic
  File "codecov_cli/services/upload/upload_collector.py", line 194, in generate_upload_data
  File "codecov_cli/services/upload/upload_collector.py", line 104, in _produce_file_fixes
  File "codecov_cli/services/upload/upload_collector.py", line 118, in _get_file_fixes
FileNotFoundError: [Errno 2] No such file or directory: 'internal/integrationtest/compile_4/testdata/ValidSketchWithNonInoBrokenSketchFileSymlink/other_file.c'
[PYI-2973:ERROR] Failed to execute script 'main' due to unhandled exception!
==> Failed to run upload-coverage
    Exiting...

What is the new behavior?

CI should succeed.

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.
✅ Project coverage is 69.35%. Comparing base (f3121a3) to head (64a6afb).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3036      +/-   ##
==========================================
+ Coverage   68.38%   69.35%   +0.97%     
==========================================
  Files         241      241              
  Lines       22734    18585    -4149     
==========================================
- Hits        15547    12890    -2657     
+ Misses       5990     4497    -1493     
- Partials     1197     1198       +1     

Flag	Coverage Δ
unit	69.35% <ø> (+0.97%)	⬆️

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