If a username, and password that produces a base64 value larger than 76 characters, base64 will add \n to the output to wrap the text. The \n is then moved to the ~/.docker/config.json, that would break build image step producing the error of
```
WARNING: Error loading config file: /root/.docker/config.json: invalid character '\n' in string literal
```
Reviewed-on: https://gitea.com/gitea/test-env/pulls/25
Reviewed-by: techknowlogick <techknowlogick@noreply.gitea.io>
Co-authored-by: James712346 <james712346@noreply.gitea.io>
Co-committed-by: James712346 <james712346@noreply.gitea.io>