patch 8.1.0255: backup test fails when using shadow directory

Problem:    Backup test fails when using shadow directory.
Solution:   Remove check for "src".

Author: brammool

src/testdir/test_backup.vim

@@ -29,7 +29,7 @@ func Test_backup2()
   sp *Xbackup.txt~
   call assert_equal(['line1', 'line2', 'line3'], getline(1,'$'))
   let f=expand('%')
-  call assert_match('src%testdir%Xbackup.txt\~', f)
+  call assert_match('%testdir%Xbackup.txt\~', f)
   bw!
   bw!
   call delete('Xbackup.txt')
@@ -49,7 +49,7 @@ func Test_backup2_backupcopy()
   sp *Xbackup.txt~
   call assert_equal(['line1', 'line2', 'line3'], getline(1,'$'))
   let f=expand('%')
-  call assert_match('src%testdir%Xbackup.txt\~', f)
+  call assert_match('%testdir%Xbackup.txt\~', f)
   bw!
   bw!
   call delete('Xbackup.txt')

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    255,
 /**/
     254,
 /**/