[Auth] Swift 6 improvements for `AuthRecaptchaVerifier` #9755

Job	Run time
changes	5s
spm-binary-cron	0s
spm-package-resolved	1m 19s
check	2m 23s
cmake-prod-db	1s
cmake	1s
sanitizers-mac	1s
pod-lib-lint	1s
sanitizers-ubuntu	1s
xcodebuild	1s
check-firestore-internal-public-headers	1s
pod-lib-lint-cron	1s
spm-binary	1s
spm-source	1s
Check all required Firestore tests results	1s
	3m 58s

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