[iOS] Exclude arm64 Simulator architecture for CommTests

Summary:
Exclude arm64 architecture for iOS Simulator.. matching what we have for the Comm target.

Allows us to run XCTests on Apple silicon machines.

Test Plan:
Ran CryptoTests from Xcode GUI and from commandline:

xcodebuild test -workspace Comm.xcworkspace -scheme Comm -destination name="iPhone 13"

Reviewers: abosh, ashoat, tomek, jacek, karol

Reviewed By: ashoat

Subscribers: adrian

Differential Revision: https://phab.comm.dev/D4622