Update to Java 21

Author: mbax

.github/workflows/build.yml

@@ -12,6 +12,6 @@ jobs:
         uses: actions/setup-java@v4
         with:
           distribution: corretto
-          java-version: 17
+          java-version: 21
       - name: Build with Maven
         run: mvn --batch-mode clean package

pom.xml

@@ -279,7 +279,7 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>3.14.0</version>
                 <configuration>
-                    <release>17</release>
+                    <release>21</release>
                 </configuration>
             </plugin>
             <plugin>
@@ -292,7 +292,7 @@
                 <artifactId>maven-javadoc-plugin</artifactId>
                 <version>${plugin.javadocs.version}</version>
                 <configuration>
-                    <source>17</source>
+                    <source>21</source>
                 </configuration>
             </plugin>
             <plugin>