patch 9.1.0706: tests: test_gettext fails when using shadow dir

patch 9.1.0706: tests: test_gettext fails when using shadow dir

Problem:  tests: test_gettext fails when using shadow dir
Solution: Link the ru_RU directory into the shadow testdir
          (James McCoy)

Link the ru_RU directory into shadow testdir

When the ru_RU locale is present, but the build is using a shadowdir,
then test_gettext_cp1251.vim and test_gettext_utf8.vim fail:

    From test_gettext_cp1251.vim:
    Executed Test_gettext()                            in   0.000848 seconds
    Executed 1 test                          in   0.007010 seconds
    1 FAILED:
    Found errors in Test_gettext():
    command line..script /home/runner/work/vim/vim/src/shadow/testdir/runtest.vim[607]..function RunTheTest[57]..Test_gettext line 9: Expected '������: ' but got 'ERROR: '

    From test_gettext_utf8.vim:
    Executed Test_gettext()                            in   0.000908 seconds
    Executed 1 test                          in   0.007339 seconds
    1 FAILED:
    Found errors in Test_gettext():
    command line..script /home/runner/work/vim/vim/src/shadow/testdir/runtest.vim[607]..function RunTheTest[57]..Test_gettext line 9: Expected '������: ' but got 'ERROR: '

This is because it's unable to load the translations from the ru_RU test
directory, since it wasn't symlinked into the shadow directory.

closes: #15591

Signed-off-by: James McCoy <jamessan@jamessan.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>