[iOS] Modified rpath for brave_rewards_ios_tests.

Added:
- /usr/lib/swift
- @executable_path/../Frameworks

This to get around the error:

brave_rewards_ios_tests.app (22597) encountered an error (Early unexpected exit, operation never finished bootstrapping - no restart will be attempted. (Underlying Error: Crash: brave_rewards_ios_tests (22597):   dyld: Using shared cache: 59E5DB8B-B935-310F-81BF-FB7488068748
Library not loaded: @rpath/libswiftCore.dylib

vendor/brave-ios/BUILD.gn

@@ -20,7 +20,7 @@ config("internal_config") {
     "-Wno-objc-property-synthesis",
     "-Wno-sign-compare",
   ]
-  ldflags = [ "-Wl,-no_compact_unwind" ]
+  ldflags = [ "-Wl,-no_compact_unwind,-rpath,/usr/lib/swift,-rpath,@executable_path/../Frameworks" ]
   include_dirs = [
     ".",
     "Ads",