Update test_git_submodules_and_add_sm_with_new_commit skip reason

This is working on Cygwin, so that old reason no longer applies.
(The test was not being skipped on Cygwin, and was passing.)

It is not working on native Windows, due to a PermissionError from
attempting to move a file that is still open (which Windows doesn't
allow). That may have been the original native Windows skip reason,
but the old AppVeyor CI link for it is broken or not public. This
makes the reason clear, though maybe I should add more details.

Author: EliahKagan

test/test_submodule.py

@@ -750,13 +750,12 @@ def test_list_only_valid_submodules(self, rwdir):
 
     @skipIf(
         HIDE_WINDOWS_KNOWN_ERRORS,
-        """FIXME on cygwin: File "C:\\projects\\gitpython\\git\\cmd.py", line 671, in execute
-                raise GitCommandError(command, status, stderr_value, stdout_value)
-            GitCommandError: Cmd('git') failed due to: exit code(128)
-              cmdline: git add 1__Xava verbXXten 1_test _myfile 1_test_other_file 1_XXava-----verbXXten
-              stderr: 'fatal: pathspec '"1__çava verböten"' did not match any files'
-             FIXME on appveyor: see https://ci.appveyor.com/project/Byron/gitpython/build/1.0.185
-                """,
+        """
+        E   PermissionError:
+        [WinError 32] The process cannot access the file because it is being used by another process:
+        'C:\\Users\\ek\\AppData\\Local\\Temp\\test_git_submodules_and_add_sm_with_new_commitu6d08von\\parent\\module'
+        -> 'C:\\Users\\ek\\AppData\\Local\\Temp\\test_git_submodules_and_add_sm_with_new_commitu6d08von\\parent\\module_moved'
+        """  # noqa: E501,
     )
     @with_rw_directory
     @_patch_git_config("protocol.file.allow", "always")