LibJS: Fix two typos in comments in AST.cpp

Userland/Libraries/LibJS/AST.cpp

@@ -797,7 +797,7 @@ static ThrowCompletionOr<ForInOfHeadState> for_in_of_head_execute(Interpreter& i
             // 5. Let exprValue be ? GetValue(exprRef).
             state.rhs_value = rhs.execute(interpreter, global_object);
 
-            // Note that since a reference stores it's environment it doesn't matter we only reset
+            // Note that since a reference stores its environment it doesn't matter we only reset
             // this after step 5. (Also we have no way of separating these steps at this point)
             // 4. Set the running execution context's LexicalEnvironment to oldEnv.
         } else {