tq: ensure we pass the correct Accept header in verify requests
tq: ensure we pass the correct Accept header in verify requests

When we perform a verify request, we need to specify a proper Accept
header along with the Content-Type header. Do so.

Hoist the setting of the headers before the code which copies headers
from the remote side, so that the remote side can override it with a
suitable header if necessary. This is required for compatibility with
some existing servers.

github/git-lfs,github/git-lfs,github/git-lfs