[Concurrency] Update expected options for --enable-experimental-concurrency

Author: DougGregor

utils/build_swift/tests/expected_options.py

@@ -503,6 +503,7 @@ class BuildScriptImplOption(_BaseOption):
     EnableOption('--distcc'),
     EnableOption('--enable-asan'),
     EnableOption('--enable-experimental-differentiable-programming'),
+    EnableOption('--enable-experimental-concurrency'),
     EnableOption('--enable-lsan'),
     EnableOption('--enable-sanitize-coverage'),
     EnableOption('--enable-tsan'),