Fix hang and zombie process on interrupt (CTRL-C). (#3057)

Author: sk1p

docs/changelog/3056.bugfix.rst

@@ -0,0 +1 @@
+Fix hang and zombie process on interrupt (CTRL-C).

src/tox/execute/local_sub_process/__init__.py

@@ -63,6 +63,8 @@ def __init__(self, options: ExecuteOptions, out: SyncWrite, err: SyncWrite, proc
 
     @property
     def exit_code(self) -> int | None:
+        # need to poll here, to make sure the returncode we get is current
+        self._process.poll()
         return self._process.returncode
 
     def interrupt(self) -> None: