apply: Ignores GIT_AUTHOR_* env vars

[craigds]

kart apply requires that the user has a gitconfig with their user details in it, even if GIT_AUTHOR_NAME, GIT_AUTHOR_EMAIL, GIT_COMMITTER_NAME, GIT_COMMITTER_EMAIL are in the environment.

To Reproduce

# This patch should apply to the 'points.tgz' repo in the kart test data
$ echo '{"kart.diff/v1+hexwkb": {"nz_pa_points_topo_150k": {"feature": [{"+": {"fid": 1307, "geom": "01010000004B9F46B66CA76540F97C998771AD41C0", "t50_fid": 2427552, "name_ascii": "changed", "macronated": "N", "name": "changed"}}]}}, "kart.patch/v1": {"authorName": "Test Testersen", "authorEmail": "tester@example.com", "message": "Rename some stuff"}}' > patch.json

$ export GIT_AUTHOR_NAME=a GIT_AUTHOR_EMAIL=a@example.com GIT_COMMITTER_NAME=a GIT_COMMITTER_EMAIL=a@example.com

$ kart apply --ref=HEAD patch.json
Error: Please tell me who you are.

Run

  git config --global user.email "you@example.com"
  git config --global user.name "Your Name"

to set your account's default identity.
Omit --global to set the identity only in this repository.

(Kart uses the same credentials and configuration as git)

Version info

happens with kart v0.12.3.dev0+ci.4975.gitb869c8ed on Linux (ubuntu) with no ~/.gitconfig file present.