Add explicit -> None on __init__

It seems to me like `--disallow-untyped-defs`, enabled in
`mypy --strict`, should have flagged this as an error.  However, from
documentation on `no-untyped-def`, `mypy` only requires
`__init__(...) -> None` when there is any argument aside from the first
`self`.  This patch follows the parenthetical recommendation from PEP
484 that `-> None` be given anyways.

References:
* https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-disallow-untyped-defs
* https://mypy.readthedocs.io/en/stable/error_code_list2.html#check-that-every-function-has-an-annotation-no-untyped-def
* https://peps.python.org/pep-0484/#the-meaning-of-annotations

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

Author: ajnelson-nist

case_utils/case_validate/__init__.py

@@ -72,7 +72,7 @@ def __init__(
         graph: Any,
         text: str,
         undefined_concepts: Set[rdflib.URIRef],
-    ):
+    ) -> None:
         self.conforms = conforms
         self.graph = graph
         self.text = text