[test] Add Python 3.10 (#480)

Authored-by: pukkandan, xtkoba

.github/workflows/core.yml

@@ -10,7 +10,7 @@ jobs:
       matrix:
         os: [ubuntu-18.04]
         # py3.9 is in quick-test
-        python-version: [3.7, 3.8, pypy-3.6, pypy-3.7]
+        python-version: [3.7, 3.8, 3.10-dev, pypy-3.6, pypy-3.7]
         run-tests-ext: [sh]
         include:
         # atleast one of the tests must be in windows

.github/workflows/download.yml

@@ -9,7 +9,7 @@ jobs:
       fail-fast: true
       matrix:
         os: [ubuntu-18.04]
-        python-version: [3.7, 3.8, 3.9, pypy-3.6, pypy-3.7]
+        python-version: [3.7, 3.8, 3.9, 3.10-dev, pypy-3.6, pypy-3.7]
         run-tests-ext: [sh]
         include:
         - os: windows-latest

yt_dlp/utils.py

@@ -3964,7 +3964,7 @@ def detect_exe_version(output, version_re=None, unrecognized='present'):
         return unrecognized
 
 
-class LazyList(collections.Sequence):
+class LazyList(collections.abc.Sequence):
     ''' Lazy immutable list from an iterable
     Note that slices of a LazyList are lists and not LazyList'''
 
@@ -6313,4 +6313,4 @@ def traverse_dict(dictn, keys, casesense=True):
 
 
 def variadic(x, allowed_types=(str, bytes)):
-    return x if isinstance(x, collections.Iterable) and not isinstance(x, allowed_types) else (x,)
+    return x if isinstance(x, collections.abc.Iterable) and not isinstance(x, allowed_types) else (x,)