Handle conditional import of SecretStr

Author: LuKrO2011

src/pynguin/utils/openai_key_resolver.py

@@ -10,8 +10,15 @@
 
 import logging
 import os
-
-from pydantic import SecretStr
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from pydantic import SecretStr
+else:
+    try:
+        from pydantic import SecretStr
+    except ImportError:
+        SecretStr = str
 
 import pynguin.configuration as config