HEPTAPOD_NO_GIT: carrying over from internal API response

As with Workhorse and direct subprocess calls, we'll need
this flag, whose effect on py-heptapod is to prevent Git
export entirely in the native case.

--HG--
branch : heptapod
4 jobs for !23 with topic/heptapod/heptapod-no-git in 3 minutes and 33 seconds (queued for 2 seconds)
detached
Status Name Job ID Coverage
  Test
passed go:1.14 #253142

00:03:30

73.1%
passed go:1.15 #253143

00:03:11

73.1%
passed go:1.16 #253144

00:03:31

73.1%
passed race #253145

00:03:13