fix: correct LocalizedError conformance

[vvisionnn]

based on the document of LocalizedError here: https://developer.apple.com/documentation/foundation/localizederror/2946895-errordescription

the errorDescription is a optional string type, the original implementation just using the fallback of the default protocol conformance

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[morganchen12]

Thanks @vvisionnn! Please sign the CLA and someone will review this PR.

[paulb777]

@vvisionnn Thanks. It looks like the change leads to several CI errors that will need to be investigated.

[ncooke3]

CI should be fixable by running

scripts/style.sh FirebaseCore/Internal/Sources/HeartbeatLogging/RingBuffer.swift

[vvisionnn]

@ncooke3 I have executed this script after I mentioned this error, but there is nothing changed, don't know why

[vvisionnn]

checked the script, looks like it is just a swiftformat command with config file at root level
just run format manually