Improve description of new build-script flags

(cherry picked from commit c8d7d13)

Author: stmontgomery

utils/build_swift/build_swift/driver_arguments.py

@@ -812,9 +812,9 @@ def create_argument_parser():
            help='build WasmKit')
 
     option('--swift-testing', toggle_true('build_swift_testing'),
-           help='build swift-testing')
+           help='build Swift Testing')
     option('--install-swift-testing', toggle_true('install_swift_testing'),
-           help='install swift-testing')
+           help='install Swift Testing')
 
     option('--xctest', toggle_true('build_xctest'),
            help='build xctest')