Make it possible to treat ExtraScriptValue as a path

This lets some plugins still work despite the breaking change

Fixes #3310

Author: oprypin

mkdocs/config/config_options.py

@@ -941,6 +941,9 @@ def __init__(self, path: str = '', config_file_path=None):
     def __str__(self):
         return self.path
 
+    def __fspath__(self):
+        return self.path
+
 
 class ExtraScript(SubConfig[ExtraScriptValue]):
     def run_validation(self, value: object) -> ExtraScriptValue: