Revert "Remove Python 3.6 support"

This reverts commit 6929b41a21.

yt_dlp/compat/asyncio.py

@@ -0,0 +1,23 @@
+# flake8: noqa: F405
+from asyncio import *  # noqa: F403
+
+from .compat_utils import passthrough_module
+
+passthrough_module(__name__, 'asyncio')
+del passthrough_module
+
+try:
+    run  # >= 3.7
+except NameError:
+    def run(coro):
+        try:
+            loop = get_event_loop()
+        except RuntimeError:
+            loop = new_event_loop()
+            set_event_loop(loop)
+        loop.run_until_complete(coro)
+
+try:
+    all_tasks  # >= 3.7
+except NameError:
+    all_tasks = Task.all_tasks