NimbusJwtDecoder unknown KID scenario is not correctly tested

[jonkjenn]

Two different methods are used for accessing the cache and only one of them is correctly mocked. This means the cache will always refresh unrelated to the unknown KID. https://github.com/spring-projects/spring-security/blob/main/oauth2/oauth2-jose/src/main/java/org/springframework/security/oauth2/jwt/NimbusJwtDecoder.java#L415
The RemoteJWKSet will never actually find a missing KID and do the update because of this. The code seems to be correct though and the test succeeds with the fixed mock.

Relates to this issue #11621

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[jzheaux]

Thanks, @jonkjenn! Will you please rebase to 5.7.x and squash your commits?

Please also add a brief description to the commit like:

Polish NimbusJwtDecoderTests

- Add missing mock

Closes gh-12238

[jonkjenn]

@jzheaux Updated