Fix default config file not found

[silvanocerza]

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• The PR has no duplicates (please search among the Pull Requests
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• Tests for the changes have been added (for bug fixes / features)
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• What kind of change does this PR introduce?
  Fixes default config file never found.

• What is the current behavior?
  Default config file is never found by the CLI.

• What is the new behavior?
  Default config file is now found correctly.

• Does this PR introduce a breaking change?
  No.

• Other information:
  Fixes [ Nightly Build Regression ] - Arduino CLI will not use the default configuration .yaml file #1018

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[rsora]

@silvanocerza is it possible to create a test (unit or integ) to catch this regression?
As we will work more on the config management in the next weeks it would be nice to enhance our safeguards in this area WDYT?

[silvanocerza]

Already solved by #1027, closing.