Update Java secure coding guidelines to SPML 1.1 schema

Co-authored-by: bren <bren@juanantonio.info>

Author: cursoragent

spml/pom.xml

@@ -8,7 +8,7 @@
   <version>0.1.0</version>
 
   <properties>
-    <java.version>24</java.version>
+    <java.version>21</java.version>
     <maven.version>3.9.10</maven.version>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>