fix: Fix list of scopes in app integrations

[jorgeajimenezl]

What kind of change does this PR introduce? (check at least one)

• [x] Bugfix
• [ ] Feature
• [ ] Code style update
• [ ] Refactor
• [ ] Other, please describe:

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

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• [x] You consent that the copyright of your pull request source code belongs to Authlib's author.

[codespearhead]

I agree with the proposed changes, as they provide a safeguard against raising an AttributeError when scope is an iterable instead of a string. However, I can't think of a case where that will ever happen.

If there is an existing issue that prompted this pull request, please link this PR to it.