feat: [TestUtilString]: Implementadel test para la clase para normalizar un título

src/test/java/com/ujaen/tfg/mangaffinity/util/TestUtilString.java

+package com.ujaen.tfg.mangaffinity.util;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class TestUtilString {
+    @Test
+    void testNormalizar() {
+        Assertions.assertThat(UtilString.normalizar(" áÁaaa    ´   OO_OO ")).isEqualTo("aaaaa oooo");
+    }
+}