fix: make the return value of accessToken nullable #804

Job	Run time
Examples	3m 34s
xcodebuild (16) (test, IOS, 16.2)	4m 40s
xcodebuild (15) (test, IOS, 15.4)	13m 43s
Library (evolution)	40s
xcodebuild (16) (test, MACOS, 16.2)	5m 18s
xcodebuild (15) (test, MAC_CATALYST, 15.4)	4m 38s
xcodebuild (16) (IOS, 16.2)	3m 44s
xcodebuild (15) (test, MACOS, 15.4)	5m 5s
xcodebuild (15) (test, TVOS, 15.4)	4m 52s
xcodebuild (16) (MACOS, 16.2)	3m 56s
xcodebuild (15) (test, VISIONOS, 15.4)	8m 33s
xcodebuild (15) (test, WATCHOS, 15.4)	4m 13s
xcodebuild (15) (IOS, 15.2)	3m 47s
xcodebuild (15) (IOS, 15.4)	4m 1s
xcodebuild (15) (MAC_CATALYST, 15.4)	4m 27s
xcodebuild (15) (MACOS, 15.2)	5m 10s
xcodebuild (15) (MACOS, 15.4)	8m 31s
xcodebuild (15) (TVOS, 15.4)	5m 57s
xcodebuild (15) (VISIONOS, 15.4)	4m 32s
xcodebuild (15) (WATCHOS, 15.4)	4m 25s
	1h 43m 46s

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