Update keycloak/keycloak Docker tag to v26.5.1

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:26.5.1@sha256:b80a48090594367bd8cf6fe2019466ac4ea49de4d0830fb2a43256eda37b18f5";
 
     private KeycloakContainer keycloak;