fix: add aria-required to s-reason field in suppressions form

The reason input had `required` for browser validation but was missing
`aria-required="true"`, so screen readers did not announce it as required.
Matches the fix already applied to the equivalent field in base.html.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/suppressions.html

@@ -51,7 +51,7 @@
             <label class="lt-label" for="s-reason">Reason <span class="required">*</span></label>
             <input type="text" class="lt-input" id="s-reason" name="reason"
                    placeholder="e.g. Planned switch maintenance, replacing SFP on large1/enp43s0"
-                   required>
+                   required aria-required="true">
           </div>
         </div>