Do not use ~ when uploading the signed hashes

~ is expanded by the shell before issuing commands (and when it isn't, it produces unwanted results, because programs don't actually expand it).

Therefore, make {tor,mullvad}browser-upload-sha256sums-{release,channel} actually use a target_dir that is resolved absolutely in your local machine, not in the remote one.

I have a different username in my machine and in TPO's LDAP. Therefore, it made the script not work.

However, since we're using paths relative to home, we can pass relative paths, as they will be resolved starting from home.