fix(api): storing cancelablles with actor methods in AppSyncRTC #318

Job	Run time
Build Amplify Swift for iOS / Build Amplify-Build \| iOS	10m 30s
Build Amplify Swift for macOS / Build Amplify-Build \| macOS	9m 24s
Build Amplify Swift for tvOS / Build Amplify-Build \| tvOS	7m 26s
Build Amplify Swift for watchOS / Build Amplify-Build \| watchOS	10m 14s
Confirm Passing Build Steps	1s
	37m 35s

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