deps: update dependency org.graalvm.buildtools:native-maven-plugin to v0.9.21 (#1705)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [org.graalvm.buildtools:native-maven-plugin](https://github.com/graalvm/native-build-tools) | `0.9.20` -> `0.9.21` | [![age](https://badges.renovateapi.com/packages/maven/org.graalvm.buildtools:native-maven-plugin/0.9.21/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/org.graalvm.buildtools:native-maven-plugin/0.9.21/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/org.graalvm.buildtools:native-maven-plugin/0.9.21/compatibility-slim/0.9.20)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/org.graalvm.buildtools:native-maven-plugin/0.9.21/confidence-slim/0.9.20)](https://docs.renovatebot.com/merge-confidence/) |

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Author: renovate-bot

samples/native-image-sample/pom.xml

@@ -99,7 +99,7 @@
           <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.bigtable.NativeImageBigtableSample