[Feature][Github] Modify test connection to verify one token per time

[warren830]

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• I had searched in the issues and found no similar feature requirement.

Description

Change api TestConnection of github plugin to validate exactly 1 token, and return username for the token if succeeded.

Use case

No response

Related issues
#2367

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[warren830]

We can use the following api to test if a token is valid
`curl --location --request GET --X GET 'https://api.github.com/user'
--header 'User-Agent: Apipost client Runtime/+https://www.apipost.cn/'
--header 'Authorization: Bearer ghp_xxx'

[warren830]

@e2corporation Hi Julien, backend has been modified, please change the config-ui to adopt this api after the pr gets merged

[Startrekzky]

Fixed.