chore(deps): update eclipse-temurin docker tag to v21

pom.xml

@@ -13,10 +13,10 @@
 
     <properties>
         <main.class>me.bobert.netneutrality.NetNeutrality</main.class>
-        <java.version>17</java.version>
+        <java.version>21</java.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>17</maven.compiler.source>
-        <maven.compiler.target>17</maven.compiler.target>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
     </properties>
 
     <build>