Fix typo in Lib/concurrent/futures/thread.py (GH-13953)

Lib/concurrent/futures/process.py

@@ -505,7 +505,7 @@ class ProcessPoolExecutor(_base.Executor):
                 worker processes will be created as the machine has processors.
             mp_context: A multiprocessing context to launch the workers. This
                 object should provide SimpleQueue, Queue and Process.
-            initializer: An callable used to initialize worker processes.
+            initializer: A callable used to initialize worker processes.
             initargs: A tuple of arguments to pass to the initializer.
         """
         _check_system_limits()

Lib/concurrent/futures/thread.py

@@ -125,7 +125,7 @@ class ThreadPoolExecutor(_base.Executor):
             max_workers: The maximum number of threads that can be used to
                 execute the given calls.
             thread_name_prefix: An optional name prefix to give our threads.
-            initializer: An callable used to initialize worker threads.
+            initializer: A callable used to initialize worker threads.
             initargs: A tuple of arguments to pass to the initializer.
         """
         if max_workers is None: