libs: use up-to-date version of Jython

despite the fact, that dcache uses Jython only for unit tests and some
debugging purposes, we need to use up-to-date versions.

see: https://github.com/dCache/dcache/security/dependabot/28

Acked-by: Paul Millar
Target: master
Require-book: no
Require-notes: yes

pom.xml

@@ -798,7 +798,7 @@
             <dependency>
                 <groupId>org.python</groupId>
                 <artifactId>jython</artifactId>
-                <version>2.5.3</version>
+                <version>2.7.3</version>
             </dependency>
         <dependency>
             <groupId>org.dcache</groupId>