Fix inline labels with a custom select (#26615)

Add an sr-only class to the label on inline labels with a custom select

docs/4.1/components/forms.md

@@ -570,7 +570,7 @@ And of course [custom form controls](#custom-forms) are supported.
 <form>
   <div class="form-row align-items-center">
     <div class="col-auto my-1">
-      <label class="mr-sm-2" for="inlineFormCustomSelect">Preference</label>
+      <label class="mr-sm-2 sr-only" for="inlineFormCustomSelect">Preference</label>
       <select class="custom-select mr-sm-2" id="inlineFormCustomSelect">
         <option selected>Choose...</option>
         <option value="1">One</option>