Explicitly include hermes.h in RCTHostTests.mm (facebook#50022)

Summary:
Pull Request resolved: facebook#50022

RCTHostTests.mm calls `makeHermesRuntime`, which is from `hermes.h`. Explicitly include the header so that RCTHostTests isn't getting it indirectly.

Changelog: [Internal]

Reviewed By: javache

Differential Revision: D71146426

fbshipit-source-id: 5a5f5a466e1920797c4531773ca23f53eb1203b7

Author: Danny Su

packages/react-native/ReactCommon/react/runtime/iostests/RCTHostTests.mm

@@ -15,6 +15,7 @@
 #import <ReactCommon/RCTHost.h>
 #import <ReactCommon/RCTInstance.h>
 #import <ReactCommon/RCTTurboModuleManager.h>
+#import <hermes/hermes.h>
 
 #import <OCMock/OCMock.h>