Squelch -Wuninitialized in TestStateMachine.cpp (#23934)

This warning has not been fixed. Squelch it to remove noisy output in
the build log.

The underlying issue is tracked at #21255
diff --git a/src/lib/support/tests/BUILD.gn b/src/lib/support/tests/BUILD.gn
index 866fd63..0c1aee8 100644
--- a/src/lib/support/tests/BUILD.gn
+++ b/src/lib/support/tests/BUILD.gn
@@ -64,7 +64,7 @@
     "-Wconversion",
 
     # TODO(#21255): work-around for SimpleStateMachine constructor issue.
-    "-Wno-error=uninitialized",
+    "-Wno-uninitialized",
   ]
 
   public_deps = [