Remove --overwrite option from CI builds

[twometresteve]

Goal

Remove the --overwrite option when uploading dsyms in overnight CI builds, as it has been removed from the CLI.

Testing

Ultimately it will only be tested in the next scheduled build.

[github-actions]

Bugsnag.framework binary size did not change - 759,192 bytes

    FILE SIZE        VM SIZE    
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  [ = ]       0  [ = ]       0    TOTAL

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