patch 8.1.0264: backup tests fail when CWD is in /tmp

Problem:    Backup tests fail when CWD is in /tmp.
Solution:   Make 'backupskip' empty. (Christian Brabandt, closes vim#3301)

src/testdir/test_backup.vim

@@ -1,7 +1,7 @@
 " Tests for the backup function
 
 func Test_backup()
-  set backup backupdir=.
+  set backup backupdir=. backupskip=
   new
   call setline(1, ['line1', 'line2'])
   :f Xbackup.txt
@@ -12,13 +12,13 @@ func Test_backup()
   let l = readfile('Xbackup.txt~')
   call assert_equal(['line1', 'line2'], l)
   bw!
-  set backup&vim backupdir&vim
+  set backup&vim backupdir&vim backupskip&vim
   call delete('Xbackup.txt')
   call delete('Xbackup.txt~')
 endfunc
 
 func Test_backup2()
-  set backup backupdir=.//
+  set backup backupdir=.// backupskip=
   new
   call setline(1, ['line1', 'line2', 'line3'])
   :f Xbackup.txt
@@ -34,11 +34,11 @@ func Test_backup2()
   bw!
   call delete('Xbackup.txt')
   call delete(f)
-  set backup&vim backupdir&vim
+  set backup&vim backupdir&vim backupskip&vim
 endfunc
 
 func Test_backup2_backupcopy()
-  set backup backupdir=.// backupcopy=yes
+  set backup backupdir=.// backupcopy=yes backupskip=
   new
   call setline(1, ['line1', 'line2', 'line3'])
   :f Xbackup.txt
@@ -54,5 +54,5 @@ func Test_backup2_backupcopy()
   bw!
   call delete('Xbackup.txt')
   call delete(f)
-  set backup&vim backupdir&vim backupcopy&vim
+  set backup&vim backupdir&vim backupcopy&vim backupskip&vim
 endfunc

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    264,
 /**/
     263,
 /**/