Update Godot.gitignore to ignore export_credentials.cfg

As of https://github.com/godotengine/godot/pull/76165, export_presets.cfg no longer contains sensitive information. Sensitive information now resides in export_credentials.cfg

Godot.gitignore

@@ -4,7 +4,7 @@
 # Godot-specific ignores
 .import/
 export.cfg
-export_presets.cfg
+export_credentials.cfg
 
 # Imported translations (automatically generated from CSV files)
 *.translation