patch 9.1.0663: tests: zip test still resets 'shellslash' option

Problem:  tests: zip test still resets 'shellslash' option
Solution: Remove resetting the 'shellslash' option, the zip
          plugin should now be able to handle this options

closes: #15434

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_zip_plugin.vim

@@ -10,8 +10,6 @@ endif
 runtime plugin/zipPlugin.vim
 
 def Test_zip_basic()
-  var _sl = &shellslash
-  set noshellslash
 
   ### get our zip file
   if !filecopy("samples/test.zip", "X.zip")
@@ -134,6 +132,4 @@ def Test_zip_basic()
 
   bw
 
-  &shellslash = _sl
-
 enddef

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    663,
 /**/
     662,
 /**/