syntax: Fix typo in Generic error code

Author: eemeli

fluent.syntax/fluent/syntax/errors.py

@@ -9,7 +9,7 @@ def __init__(self, code: str, *args: Union[str, None]):
 
 
 def get_error_message(code: str, args: Tuple[Union[str, None], ...]) -> str:
-    if code == "E00001":
+    if code == "E0001":
         return "Generic error"
     if code == "E0002":
         return "Expected an entry start"