Wrap _listeners access with _realtimeLockQueue in fetchLatestConfig completionHandler #3671

Job	Run time
remoteconfig (iOS)	27m 49s
pod-lib-lint (ios, FirebaseRemoteConfig.podspec, macos-14)	4m 45s
pod-lib-lint (tvos, FirebaseRemoteConfig.podspec, macos-14)	3m 38s
pod-lib-lint (macos --skip-tests, FirebaseRemoteConfig.podspec, macos-14)	4m 28s
pod-lib-lint (watchos, FirebaseRemoteConfig.podspec, macos-14)	4m 6s
catalyst	7m 45s
quickstart	1m 37s
spm-package-resolved	55s
sample-build-test	5m 27s
spm (iOS, macos-14, Xcode_15.2)	14m 23s
spm (iOS, macos-14, Xcode_16)	19m 45s
spm (tvOS, macos-14, Xcode_15.2)	7m 50s
spm (tvOS, macos-14, Xcode_16)	9m 3s
spm (macOS, macos-14, Xcode_15.2)	6m 9s
spm (macOS, macos-14, Xcode_16)	6m 52s
spm (catalyst, macos-14, Xcode_15.2)	7m 0s
spm (catalyst, macos-14, Xcode_16)	9m 1s
spm (watchOS, macos-14, Xcode_15.2)	8m 45s
spm (watchOS, macos-14, Xcode_16)	7m 35s
remoteconfig-cron-only	0s
	2h 36m 53s

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