Constrain isodate import to Py<3.11

Author: dalito

linkml_runtime/utils/metamodelcore.py

@@ -7,7 +7,6 @@
 from typing import Union, Optional
 from urllib.parse import urlparse
 
-import isodate
 from rdflib import Literal, BNode, URIRef
 from rdflib.namespace import is_ncname
 from rdflib.term import Identifier as rdflib_Identifier
@@ -19,6 +18,9 @@
 from linkml_runtime.utils.uri_validator import validate_uri_reference
 from linkml_runtime.utils.uri_validator import validate_curie
 
+if sys.version_info < (3, 11):
+    import isodate
+
 # Reference Decimal to make sure it stays in the imports
 _z = Decimal(1)