Update keycloak/keycloak Docker tag to v26.5.2

Author: renovate[bot]

src/test/java/plugins/OicAuthPluginTest.java

@@ -45,7 +45,7 @@ public class OicAuthPluginTest extends AbstractJUnitTest {
     private static final String CLIENT = "jenkins";
 
     private static final String KEYCLOAK_IMAGE =
-            "keycloak/keycloak:26.4.7@sha256:9409c59bdfb65dbffa20b11e6f18b8abb9281d480c7ca402f51ed3d5977e6007";
+            "keycloak/keycloak:26.5.2@sha256:fb31a59deb46f746f2aaa25adc5da39ceccac4fd22d36a519562b0bf02e8df20";
 
     private KeycloakContainer keycloak;