The underlying implementation of os.exec uses channels and goroutines.
It is possible to have time-variant error values returned from Cmd.Wait
depending on which comes first.

Also, the git subcommand and options should be separated tokens.

Fixes a flaky test in modules/git/command_test.go

* move code.gitea.io/git to code.gitea.io/gitea/modules/git

* fix imports

* fix fmt

* fix misspell

* remove wrong tests data

* fix unit tests

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* enable Debug to trace the failure tests

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* comment commit count tests since git clone depth is 50

* fix tests

* update from code.gitea.io/git

* revert change to makefile