Updated some POM items

Note that there is an issue with Spigot 1.20.6 or later where ItemType
cannot be mocked for some reason.

pom.xml

@@ -55,12 +55,12 @@
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
-        <java.version>17</java.version>
+        <java.version>21</java.version>
         <!-- Non-minecraft related dependencies -->
         <powermock.version>2.0.9</powermock.version>
         <!-- More visible way how to change dependency versions -->
-        <spigot.version>1.20.3-R0.1-SNAPSHOT</spigot.version>
-        <bentobox.version>2.0.0-SNAPSHOT</bentobox.version>
+        <spigot.version>1.20.4-R0.1-SNAPSHOT</spigot.version>
+        <bentobox.version>2.4.1-SNAPSHOT</bentobox.version>
         <!-- Revision variable removes warning about dynamic version -->
         <revision>${build.version}-SNAPSHOT</revision>
         <!-- Do not change unless you want different name for local builds. -->