Update UNIX-like system user profile picture with its GitHub account's one
try:
    ...
except Exception:
    raise
else:
    ...

You're not doing anything with the captured exception, so this accomplish nothing more than the code in .... You can drop the try, the code in the else will never execute if there is an exception in the previous two functions anyway.
Depending on the size of the downloaded images, you may also consider streaming the http response to a file directly instead of using the memory as a buffer.