chore: fix spring login example code (vaadin#3572)

Example code cannot be compiled, since it misses a throws statement.

Author: mcollovati

articles/hilla/lit/guides/security/spring-login.adoc

@@ -50,7 +50,7 @@ public class SecurityConfig extends VaadinWebSecurity {
   }
 
   @Override
-  protected void configure(HttpSecurity http) {
+  protected void configure(HttpSecurity http) throws Exception {
     // Set default security policy that permits Hilla internal requests and
     // denies all other
     http.authorizeHttpRequests(registry -> registry.requestMatchers(
@@ -85,7 +85,7 @@ Public views need to be added to the configuration before calling [methodname]`s
 [source,java]
 ----
   @Override
-  protected void configure(HttpSecurity http) {
+  protected void configure(HttpSecurity http) throws Exception {
     http.authorizeHttpRequests(registry -> {
         registry.requestMatchers(new AntPathRequestMatcher("/public-view")).permitAll(); // custom matcher
     });