Update __init__.py - change to 2.2.0 for release (projectmesa#1951)

The current deploy process uses this line for generating the version.

mesa/__init__.py

@@ -25,7 +25,7 @@
 ]
 
 __title__ = "mesa"
-__version__ = "2.3.0-dev"
+__version__ = "2.2.0"
 __license__ = "Apache 2.0"
 _this_year = datetime.datetime.now(tz=datetime.timezone.utc).date().year
 __copyright__ = f"Copyright {_this_year} Project Mesa Team"