chore: bump api version

Event api requires endstone api version 0.4

Author: wu-vincent

src/endstone_example/example_listener.py

@@ -4,7 +4,6 @@
 
 
 class ExampleListener:
-
     def __init__(self, plugin: Plugin):
         self._plugin = plugin
 

src/endstone_example/example_plugin.py

@@ -9,7 +9,7 @@
 class ExamplePlugin(Plugin):
     name = "PythonExamplePlugin"
     version = "0.4.0"
-    api_version = "0.3"
+    api_version = "0.4"
     description = "Python example plugin for Endstone servers"
     authors = ["Endstone Developers <hello@endstone.dev>"]
     website = "https://github.com/EndstoneMC/python-example-plugin"