[Makefile] Include setup.cfg in the tarball (closes #14857)

Makefile

@@ -124,5 +124,5 @@ youtube-dl.tar.gz: youtube-dl README.md README.txt youtube-dl.1 youtube-dl.bash-
 		bin devscripts test youtube_dl docs \
 		ChangeLog LICENSE README.md README.txt \
 		Makefile MANIFEST.in youtube-dl.1 youtube-dl.bash-completion \
-		youtube-dl.zsh youtube-dl.fish setup.py \
+		youtube-dl.zsh youtube-dl.fish setup.py setup.cfg \
 		youtube-dl