fixup: Insert "and async functions" into note re execution contexts

spec.html

@@ -11746,7 +11746,7 @@ <h1>Execution Contexts</h1>
       <h1>Execution Context Stack</h1>
       <p>An agent's <dfn id="execution-context-stack" variants="execution context stacks">execution context stack</dfn> is used to organize some or all of the agent's execution contexts. The running execution context is always the top element of this stack.</p>
       <p>Adding and removing always happens at the “top” of the execution context stack. When an execution context is added, it becomes the topmost (i.e., the running execution context), and when it is later removed, the execution context “below” it becomes topmost again.</p>
-      <emu-note>In the absense of generators, every execution context that is pushed onto the stack is new, and when it's removed from the stack it can be discarded. With generators, some execution contexts outlive their time on the stack, exist for a while outside the stack, and then later are pushed onto the stack again.</emu-note>
+      <emu-note>In the absence of generators and async functions, every execution context that is pushed onto the stack is new, and when it's removed from the stack it can be discarded. With generators and async functions, some execution contexts outlive their time on the stack, exist for a while outside the stack, and then later are pushed onto the stack again.</emu-note>
     </emu-clause>
 
     <emu-clause id="sec-getactivescriptormodule" type="abstract operation">