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What kind of change does this PR introduce?

Bug fix

What is the current behavior?

When a client archives a sketch via gRPC and the archiveTarget already exists, the CLI correctly errors, but with the incorrect status code. The status code is 3 (illegal argument) instead of 6 (already exists).
Currently, clients must parse the error message if they want to handle the archive -> fail -> archive with override flow. This might not work reliably with translations.

What is the new behavior?

The CLI errors with the correct already exists status code when archiving a sketch, and the archive target already exists.

Does this PR introduce a breaking change, and istitled accordingly?

Actually, this is a breaking change, but I do not know if any client is explicitly handling status code 3. The Arduino IDE 2.x just wipes the target if it exists:https://github.com/arduino/arduino-ide/blob/4d6cfad0ff603a106efd68ffe015d6fc7449f5fc/arduino-ide-extension/src/node/sketches-service-impl.ts#L637-L639

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