fix: correct type hint for Value

Author: m-xim

textcompose/core/types.py

@@ -5,5 +5,5 @@
 if TYPE_CHECKING:
     from textcompose.core.component import Component  # type: ignore[unused-import]
 
-Value = Union[MagicFilter, str, Callable[[Mapping[str, Any]], str | None], "Component"]
+Value = Union[MagicFilter, str, Callable[[Mapping[str, Any]], Union[str, None]], "Component"]
 Condition = Union[MagicFilter, Callable[[Mapping[str, Any]], bool], bool, str, "Component"]