zephyr: errno: handle unknown values

Handle unknown errno values when converting to a string, instead of
raising an exception.

Signed-off-by: Jordan Yates <jordan@embeint.com>

Author: JordanYates

src/infuse_iot/zephyr/errno.py

@@ -104,4 +104,7 @@ def __new__(cls, value: int, description: str = ""):
 
     @classmethod
     def strerror(cls, int) -> str:
-        return cls(int).description
+        try:
+            return cls(int).description
+        except ValueError:
+            return f"Unknown errno ({int})"