[google_maps_flutter_ios] Exclude from Xcode analysis until upstream warning is fixed (#11480)

Adds `google_maps_flutter_ios` to the Xcode warnings exceptions list to fix
the CI analyze failure caused by a `-Wenum-enum-conversion` warning in the
`Google-Maps-iOS-Utils` CocoaPods dependency.

Upstream issue: googlemaps/google-maps-ios-utils#570
Fixes: flutter/flutter#184470

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Author: okorohelijah

script/configs/xcode_warnings_exceptions.yaml

@@ -7,3 +7,7 @@
 # TODO(loicsharma): Remove once AppAuth-iOS's warnings are fixed.
 # See: https://github.com/flutter/flutter/issues/162342
 - google_sign_in_ios
+
+# TODO(okorohelijah): Remove once Google-Maps-iOS-Utils's warnings are fixed upstream.
+# See: https://github.com/flutter/flutter/issues/184470
+- google_maps_flutter_ios