CCM-10548: updated aria tag

Author: mark-r-bjss

frontend/src/__tests__/components/forms/LetterTemplateForm.test.tsx/__snapshots__/LetterTemplateForm.test.tsx.snap

@@ -2247,6 +2247,7 @@ exports[`renders page with preloaded field values 1`] = `
             </select>
           </div>
           <div
+            aria-live="assertive"
             class="nhsuk-warning-callout"
             data-testid="rtl-language-warning"
           >
@@ -2699,6 +2700,7 @@ exports[`shows right-to-left language warning when language changes 1`] = `
             </select>
           </div>
           <div
+            aria-live="assertive"
             class="nhsuk-warning-callout"
             data-testid="rtl-language-warning"
           >

frontend/src/components/forms/LetterTemplateForm/LetterTemplateForm.tsx

@@ -181,7 +181,10 @@ export const LetterTemplateForm: FC<
 
               {letterTemplateLanguage &&
                 isRightToLeft(letterTemplateLanguage) && (
-                  <WarningCallout data-testid='rtl-language-warning'>
+                  <WarningCallout
+                    data-testid='rtl-language-warning'
+                    aria-live='assertive'
+                  >
                     <WarningCallout.Label>
                       {rtlWarning.heading}
                     </WarningCallout.Label>