Update SNAPSHOT version to v2.21.0

Author: gridsuite-actions[bot]

pom.xml

@@ -19,7 +19,7 @@
 
     <groupId>org.gridsuite</groupId>
     <artifactId>gridsuite-voltage-init-server</artifactId>
-    <version>2.20.0-SNAPSHOT</version>
+    <version>2.21.0-SNAPSHOT</version>
 
     <packaging>jar</packaging>
     <name>Voltage init server</name>