Spelling fixes to docs, docstrings, and comments (GH-6374)

(cherry picked from commit 61f82e0e337f971da57f8f513abfe693edf95aa5)

Co-authored-by: Ville Skyttä <ville.skytta@iki.fi>
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index bff1dc2..44501d9 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -5948,7 +5948,7 @@
 @unittest.skipUnless(sys.platform.startswith("win"), "requires Windows")
 class TestMSWindowsTCPFlags(unittest.TestCase):
     knownTCPFlags = {
-                       # avaliable since long time ago
+                       # available since long time ago
                        'TCP_MAXSEG',
                        'TCP_NODELAY',
                        # available starting with Windows 10 1607