patch 8.1.0653: arglist test fails on MS-windows

Problem:    Arglist test fails on MS-windows.
Solution:   Only use a file name with a double quote on Unix.
diff --git a/src/testdir/test_arglist.vim b/src/testdir/test_arglist.vim
index 72e727f..ad44a85 100644
--- a/src/testdir/test_arglist.vim
+++ b/src/testdir/test_arglist.vim
@@ -218,9 +218,12 @@
 endfunc
 
 func Test_args_with_quote()
-  args \"foobar
-  call assert_equal('"foobar', argv(0))
-  %argdelete
+  " Only on Unix can a file name include a double quote.
+  if has('unix')
+    args \"foobar
+    call assert_equal('"foobar', argv(0))
+    %argdelete
+  endif
 endfunc
 
 " Test for 0argadd and 0argedit