Fix validation errors not being flashed correctly

src/Application.ts

@@ -107,7 +107,7 @@ export default abstract class Application implements Extendable<ApplicationCompo
                         res.send('Error: ' + err.getMessages());
                     },
                     html: () => {
-                        req.flash('validation', err.getMessages().toString());
+                        req.flash('validation', err.getMessages());
                         res.redirectBack();
                     },
                 });

src/types/Express.d.ts

@@ -24,7 +24,7 @@ declare global {
 
             flash(message: string): unknown[];
 
-            flash(event: string, message: string): void;
+            flash(event: string, message: unknown): void;
         }
 
         export interface Response {