Re-refresh to restore state after refresh tests

For #1811. This is the simple way to do it. This relies on
git.refresh working when called when no arguments, so if that ever
breaks, then it may be difficult or inefficient to investigate. But
this is simpler than any alternatives that are equally or more
robust.

This is already better than the previous incomplete way that only
restored Git.GIT_PYTHON_GIT_EXECUTABLE (and nothing in FetchInfo).
Furthermore, because the tests already depend to a large extent on
git.refreh working when called with no arguments, as otherwise the
initial refresh may not have set Git.GIT_PYTHON_GIT_EXECUTABLE
usably, it might not be worthwhile to explore other approaches.

test/test_git.py

@@ -45,12 +45,12 @@ def _patch_out_env(name):
 
 
 @contextlib.contextmanager
-def _restore_git_executable():
+def _rollback_refresh():
     old_git_executable = Git.GIT_PYTHON_GIT_EXECUTABLE
     try:
-        yield old_git_executable  # Let test code run that may rebind the attribute.
+        yield old_git_executable  # Let test code run that may mutate class state.
     finally:
-        Git.GIT_PYTHON_GIT_EXECUTABLE = old_git_executable
+        refresh()
 
 
 @ddt.ddt
@@ -319,7 +319,7 @@ def test_refresh_bad_absolute_git_path(self):
         absolute_path = str(Path("yada").absolute())
         expected_pattern = rf"\n[ \t]*cmdline: {re.escape(absolute_path)}\Z"
 
-        with _restore_git_executable() as old_git_executable:
+        with _rollback_refresh() as old_git_executable:
             with self.assertRaisesRegex(GitCommandNotFound, expected_pattern):
                 refresh(absolute_path)
             self.assertEqual(self.git.GIT_PYTHON_GIT_EXECUTABLE, old_git_executable)
@@ -328,15 +328,15 @@ def test_refresh_bad_relative_git_path(self):
         absolute_path = str(Path("yada").absolute())
         expected_pattern = rf"\n[ \t]*cmdline: {re.escape(absolute_path)}\Z"
 
-        with _restore_git_executable() as old_git_executable:
+        with _rollback_refresh() as old_git_executable:
             with self.assertRaisesRegex(GitCommandNotFound, expected_pattern):
                 refresh("yada")
             self.assertEqual(self.git.GIT_PYTHON_GIT_EXECUTABLE, old_git_executable)
 
     def test_refresh_good_absolute_git_path(self):
         absolute_path = shutil.which("git")
 
-        with _restore_git_executable():
+        with _rollback_refresh():
             refresh(absolute_path)
             self.assertEqual(self.git.GIT_PYTHON_GIT_EXECUTABLE, absolute_path)
 
@@ -345,7 +345,7 @@ def test_refresh_good_relative_git_path(self):
         dirname, basename = osp.split(absolute_path)
 
         with cwd(dirname):
-            with _restore_git_executable():
+            with _rollback_refresh():
                 refresh(basename)
                 self.assertEqual(self.git.GIT_PYTHON_GIT_EXECUTABLE, absolute_path)