Docs: fix sentence in 'Scrolling long content' modal section (twbs#39378

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Co-authored-by: Julien Déramond <juderamond@gmail.com>

site/content/docs/5.3/components/modal.md

@@ -218,7 +218,7 @@ When modals become too long for the user's viewport or device, they scroll indep
   </button>
 </div>
 
-You can also create a scrollable modal that allows scroll the modal body by adding `.modal-dialog-scrollable` to `.modal-dialog`.
+You can also create a scrollable modal that allows scrolling the modal body by adding `.modal-dialog-scrollable` to `.modal-dialog`.
 
 <div class="modal fade" id="exampleModalScrollable" tabindex="-1" aria-labelledby="exampleModalScrollableTitle" aria-hidden="true">
   <div class="modal-dialog modal-dialog-scrollable">