closes #4329

The main intention of this PR is bumping charset-normalizer to the latest version, which fixes the broken charset detection in HTTP requests without charset data in the content-type header, which has previously often lead to broken HLS playlist contents.

The pycountry source-dist tarball did not get bumped in this commit, because it would require additional changes in the installer's build script. Doesn't really matter though.

I will probably also publish a new AppImage release (3.1.1-2) with bumped dependencies. Deps get always bumped there on each release, but since charset-normalizer is a transitive dependency of streamlink, publishing a new patch release here would only make sense if we add it to streamlink's own dependencies list.