Fix a switch test that expects to an error due to read-only, but

From: David Rothenberger <d.rothenberger@entomo.com>

doesn't because the user has Administrator privileges.
---
 subversion/tests/cmdline/switch_tests.py |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/subversion/tests/cmdline/switch_tests.py b/subversion/tests/cmdline/switch_tests.py
index f71ec73..fd9be77 100755
--- a/subversion/tests/cmdline/switch_tests.py
+++ b/subversion/tests/cmdline/switch_tests.py
@@ -773,6 +773,13 @@ def refresh_read_only_attribute(sbox):
     if os.geteuid() == 0:
       raise svntest.Skip('Test doesn\'t work as uid 0')
 
+  # Same test, but for Cygwin
+  if os.name == 'posix':
+    try:
+      os.getgroups.index(513)
+    except:
+      raise svntest.Skip('Test doesn\'t work as Cygwin admin')
+
   sbox.build()
   wc_dir = sbox.wc_dir
 
