Remove unnecessary casts (#446)

* Remove unnecessary casts

Since incremental has been released, we have type hints for it now.

* Add news fragment

src/towncrier/_project.py

@@ -12,7 +12,6 @@
 
 from importlib import import_module
 from types import ModuleType
-from typing import cast
 
 from incremental import Version
 
@@ -52,7 +51,7 @@ def get_version(package_dir: str, package: str) -> str:
         return version.strip()
 
     if isinstance(version, Version):
-        return cast(str, version.base().strip())
+        return version.base().strip()
 
     if isinstance(version, tuple):
         return ".".join(map(str, version)).strip()
@@ -79,6 +78,6 @@ def get_project_name(package_dir: str, package: str) -> str:
 
     if isinstance(version, Version):
         # Incremental has support for package names
-        return cast(str, version.package)
+        return version.package
 
     raise TypeError(f"Unsupported type for __version__: {type(version)}")