fix: make version extension optional

(cherry picked from commit 52e819b1c1063c38017b0f37ac4cd5d47a576bb2)

tools/release/setup_version.py

@@ -22,7 +22,7 @@ class Version:
     major: str
     minor: str
     patch: str
-    ext: str
+    ext: Optional[str] = None
 
     def bump_ext_version(self) -> None:
         if not self.ext: