Fix AEAD algorithm documentation to indicate when AuthenticationTagMismatchException is thrown

[vcsjones]

Summary

Starting in .NET 8, AEAD algorithms throw AuthenticationTagMismatchException to indicate that decryption failed because of the authentication tag mismatch. This is a sub-type of CryptographicException, so it was not considered a breaking change.

This clarifies in the documentation that starting in .NET 8, users should expect this exception when the authentication tag does not match during decryption.

Fixes #10465

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-security, @vcsjones

[gewarren]

Thank you!

[learn-build-service-prod]

Learn Build status updates of commit 2dc41e7:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Security.Cryptography/AesCcm.xml	✅Succeeded	View
xml/System.Security.Cryptography/AesGcm.xml	✅Succeeded	View
xml/System.Security.Cryptography/ChaCha20Poly1305.xml	✅Succeeded	View

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