Update snapcraft source url (#7372)

Author: Siedlerchr

snap/snapcraft.yaml

@@ -52,7 +52,7 @@ environment:
 parts:
   jabref:
     plugin: dump
-    source: https://builds.jabref.org/master/JabRef-5.2-portable_linux.tar.gz
+    source: https://builds.jabref.org/master/JabRef-5.3-portable_linux.tar.gz
     stage-packages:
       - x11-utils
     override-build: |