Update modernizer target to Java 21

We are using Java 21, let's tell modernizer-maven-plugin that.

Change-Id: I0a47507eab69f1c2e20f7dc2a73347204a03dcbc
Signed-off-by: Robert Varga <[email protected]>

Author: rovarga

odlparent/pom.xml

@@ -76,7 +76,7 @@
     <!-- Target release for modernizer-maven-plugin. It defaults to '1.11',
          meaning Java 11, but can be set to any version in pom.xml of project
          which desires to override it (such as '1.12' for Java 12). -->
-    <odlparent.modernizer.target>1.17</odlparent.modernizer.target>
+    <odlparent.modernizer.target>1.21</odlparent.modernizer.target>
 
     <!-- Opt-out from spotbugs-maven-plugin failing the build on violations. Defaults
          to true. Set to 'false' in pom.xml of project which desires to not enforce