Be mindful of safe.bareRepository in the tests

As of Git v2.38.0, there is an option to prevent Git from accessing bare
repositories unless asked for explicitly (via `--git-dir` or `GIT_DIR`):
`safe.bareRepository`.

The tests of `git sizer`, however, assume that Git will access a bare
repository when the current directory points inside that repository.
This only works if `safe.bareRepository` indicates that this is safe.

If that is not the case, i.e. if `safe.bareRepository` is set to
`explicit`, Git demands that the environment variable `GIT_DIR` is set
(either explicitly, or via `--git-dir`) when accessing bare
repositories.

So let's set `GIT_DIR` for the test cases that work on bare
repositories.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

git_sizer_test.go

@@ -272,7 +272,10 @@ func TestRefSelections(t *testing.T) {
 				args := []string{"--show-refs", "--no-progress", "--json", "--json-version=2"}
 				args = append(args, p.args...)
 				cmd := exec.Command(executable, args...)
-				cmd.Dir = repo.Path
+				cmd.Env = append(
+					os.Environ(),
+					"GIT_DIR="+repo.Path,
+				)
 				var stdout bytes.Buffer
 				cmd.Stdout = &stdout
 				var stderr bytes.Buffer
@@ -519,7 +522,10 @@ References (included references marked with '+'):
 
 				args := append([]string{"--show-refs", "-v", "--no-progress"}, p.args...)
 				cmd := exec.Command(executable, args...)
-				cmd.Dir = repo.Path
+				cmd.Env = append(
+					os.Environ(),
+					"GIT_DIR="+repo.Path,
+				)
 				var stdout bytes.Buffer
 				cmd.Stdout = &stdout
 				var stderr bytes.Buffer