Use Path.unlink instead of os.unlink to tolerate deleted lockfiles

This should prevent issues like
#232 from appearing

pytest_container/container.py

@@ -1092,7 +1092,9 @@ def launch_container(self) -> None:
         def release_lock() -> None:
             _logger.debug("Releasing lock %s", lock.lock_file)
             lock.release()
-            os.unlink(lock.lock_file)
+            # we're fine with another process/thread having deleted the
+            # lockfile, as long as the locking was thread safe
+            Path(lock.lock_file).unlink(missing_ok=True)
 
         # Container preparation can fail, but then we would never release the
         # lock as release_lock is not yet in self._stack. However, we do not