Bump to 6.4.0 for new add specific relationship feature

Author: csprance

addons/gecs/plugin.cfg

@@ -2,5 +2,5 @@
 name="GECS"
 description="GECS - Godot Entity Component System"
 author="Quantum Tangent Games"
-version="6.3.0"
+version="6.4.0"
 script="plugin.gd"