Summary:
Fix entails using non-synthesized getter, such that underlying backing is an std::atomic<RCTNetworkTaskStatus>.
In the greater scheme of things, I believe `RCTNetworkTask` should be improved as it has several `nonatomic` properties that are read and written to on different threads. Thread safety of this class seems to have been addressed on a per property basis, judging from the employment of `std::mutex` elsewhere in the implementation.
This is an attempt at fixing https://github.com/facebook/react-native/issues/44687.
## Changelog:
[iOS][FIXED] - Fix data race related to access on `RCTNetworkTask.status`.
Pull Request resolved: https://github.com/facebook/react-native/pull/44694
Test Plan: Added unit test in class `RCTNetworkTaskTests`.
Reviewed By: cortinico
Differential Revision: D59217353
Pulled By: javache
fbshipit-source-id: 1af77238ddd99db21e2e53f174a81e207d5832b2
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