Use const instead of let

Co-authored-by: Keith Dahlby <[email protected]>

src/index.ts

@@ -796,7 +796,7 @@ export class ValidationService {
             // Because the submitter is not propagated when calling
             // form.submit(), we recreate it here.
             const submitter = submitEvent.submitter;
-            let initialFormAction = form.action;
+            const initialFormAction = form.action;
             if (submitter) {
                 const name = submitter.getAttribute('name');
                 // If name is null, a submit button is not submitted.