deps: update dependency org.graalvm.buildtools:native-maven-plugin to v0.9.21

Author: renovate-bot

samples/native-image/pom.xml

@@ -130,7 +130,7 @@
           <plugin>
             <groupId>org.graalvm.buildtools</groupId>
             <artifactId>native-maven-plugin</artifactId>
-            <version>0.9.20</version>
+            <version>0.9.21</version>
             <extensions>true</extensions>
             <configuration>
               <mainClass>com.example.spanner.NativeImageSpannerSample</mainClass>