Add aria-hidden to content warning field when dimmed so that it is not confusing to screen reader users (#22568)

app/javascript/mastodon/features/compose/components/compose_form.js

@@ -225,7 +225,7 @@ class ComposeForm extends ImmutablePureComponent {
 
         <ReplyIndicatorContainer />
 
-        <div className={`spoiler-input ${this.props.spoiler ? 'spoiler-input--visible' : ''}`} ref={this.setRef}>
+        <div className={`spoiler-input ${this.props.spoiler ? 'spoiler-input--visible' : ''}`} ref={this.setRef} aria-hidden={!this.props.spoiler}>
           <AutosuggestInput
             placeholder={intl.formatMessage(messages.spoiler_placeholder)}
             value={this.props.spoilerText}