patch 9.0.1008: test for swapfilelist() fails on MS-Windows

Problem:    Test for swapfilelist() fails on MS-Windows.
Solution:   Only check the tail of the path.  Mark a test as flaky.
diff --git a/src/testdir/test_swap.vim b/src/testdir/test_swap.vim
index c776ca5..7532655 100644
--- a/src/testdir/test_swap.vim
+++ b/src/testdir/test_swap.vim
@@ -111,16 +111,18 @@
   let fname = s:swapname()
   call assert_match('Xswapinfo', fname)
 
+  " Check the tail appears in the list from swapfilelist().  The path depends
+  " on the system.
+  let tail = fnamemodify(fname, ":t")->fnameescape()
   let nr = 0
   for name in swapfilelist()
-    if name =~ '[\\/]' .. fname .. '$'
+    if name =~ tail .. '$'
       let nr += 1
     endif
   endfor
-  call assert_equal(1, nr)
+  call assert_equal(1, nr, 'not found in ' .. string(swapfilelist()))
 
   let info = fname->swapinfo()
-
   let ver = printf('VIM %d.%d', v:version / 100, v:version % 100)
   call assert_equal(ver, info.version)