set spring boot plugin version explicitly

Author: jerrinot

kafka-questdb-connector-samples/stocks/pom.xml

@@ -79,6 +79,7 @@
             <plugin>
                 <groupId>org.springframework.boot</groupId>
                 <artifactId>spring-boot-maven-plugin</artifactId>
+                <version>${spring.boot.version}</version>
                 <configuration>
                     <mainClass>io.questdb.kafka.samples.StocksApp</mainClass>
                 </configuration>