Make `JWTError` `Sendable` #457

Job	Run time
linux-integration	3m 22s
unit-tests / dependency-graph	0s
unit-tests / api-breakage	1m 44s
unit-tests / code-coverage	2m 34s
unit-tests / gh-codeql	0s
unit-tests / linux-unit (swift:5.8-jammy)	31s
unit-tests / linux-unit (swift:5.9-jammy)	6m 22s
unit-tests / macos-unit (macos-13, ~14.3)	15s
unit-tests / linux-unit (swift:5.10-jammy)	4m 53s
unit-tests / macos-unit (macos-14, latest)	6m 32s
unit-tests / linux-unit (swiftlang/swift:nightly-6.0-jammy)	7m 15s
unit-tests / linux-unit (swiftlang/swift:nightly-main-jammy)	7m 31s
	40m 59s

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