#295 safely acces grant_types_supported

[LindezaGrey]

Pull request as discussed in https://github.com/frankie567/httpx-oauth/issues/295

[codecov[bot]]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage :thumbsup:

Coverage data is based on head (5a63319) compared to base (ab3d701). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #296 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 17 17 Lines 437 437 ========================================= Hits 437 437 ``` | [Impacted Files](https://codecov.io/gh/frankie567/httpx-oauth/pull/296?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Fran%C3%A7ois+Voron) | Coverage Δ | | |---|---|---| | [httpx\_oauth/clients/openid.py](https://codecov.io/gh/frankie567/httpx-oauth/pull/296/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Fran%C3%A7ois+Voron#diff-aHR0cHhfb2F1dGgvY2xpZW50cy9vcGVuaWQucHk=) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Fran%C3%A7ois+Voron). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Fran%C3%A7ois+Voron)

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[frankie567]

Good, thanks 🙏

@all-contributors add @LindezaGrey for code

[allcontributors[bot]]

@frankie567

I've put up a pull request to add @LindezaGrey! :tada: