Ignore rsync errors on uploading

[koppor]

We sometimes have "no space left on device" during uploading:

We can ignore this error, because it is not cruicial for the build itself.

We need to use || true, because there is no native support to ignore failures - actions/runner#2347

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• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
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• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

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