patch 8.1.0354: packadd test fails on MS-Windows

Problem:    Packadd test fails on MS-Windows.
Solution:   Ignore difference between forward and backward slashes.
diff --git a/src/testdir/test_packadd.vim b/src/testdir/test_packadd.vim
index f511a4d..6d0565b 100644
--- a/src/testdir/test_packadd.vim
+++ b/src/testdir/test_packadd.vim
@@ -53,9 +53,10 @@
   call assert_match('/testdir/Xdir/pack/mine/opt/mytest\($\|,\)', &rtp)
 
   let new_after = match(&rtp, '/testdir/Xdir/pack/mine/opt/mytest/after,')
-  let old_after = match(&rtp, ',' . first_after_entry . '\>')
+  let forwarded = substitute(first_after_entry, '\\', '[/\\\\]', 'g')
+  let old_after = match(&rtp, ',' . forwarded . '\>')
   call assert_true(new_after > 0, 'rtp is ' . &rtp)
-  call assert_true(old_after > 0, 'rtp is ' . &rtp)
+  call assert_true(old_after > 0, 'match ' . forwarded . ' in ' . &rtp)
   call assert_true(new_after < old_after, 'rtp is ' . &rtp)
 
   " NOTE: '/.../opt/myte' forwardly matches with '/.../opt/mytest'
diff --git a/src/version.c b/src/version.c
index 840f288..480d20e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    354,
+/**/
     353,
 /**/
     352,