[Glitch] Add aria-hidden to content warning field when dimmed so that it is not confusing to screen reader users

Port 83888739fd to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/features/compose/components/compose_form.js

@@ -310,7 +310,7 @@ class ComposeForm extends ImmutablePureComponent {
 
         <ReplyIndicatorContainer />
 
-        <div className={`spoiler-input ${spoiler ? 'spoiler-input--visible' : ''}`} ref={this.setRef}>
+        <div className={`spoiler-input ${spoiler ? 'spoiler-input--visible' : ''}`} ref={this.setRef} aria-hidden={!this.props.spoiler}>
           <AutosuggestInput
             placeholder={intl.formatMessage(messages.spoiler_placeholder)}
             value={spoilerText}