deps: update dependency org.springframework.boot:spring-boot-maven-plugin to v2.6.4 (#822)

Author: renovate-bot

samples/spring-framework/pom.xml

@@ -19,7 +19,7 @@ limitations under the License.
   <properties>
     <maven.compiler.target>1.8</maven.compiler.target>
     <maven.compiler.source>1.8</maven.compiler.source>
-    <spring.version>2.6.3</spring.version>
+    <spring.version>2.6.4</spring.version>
   </properties>
 
   <!--