patch 9.1.0721: tests: test_mksession does not consider XDG_CONFIG_HOME

Problem:  tests: test_mksession does not consider XDG_CONFIG_HOME
Solution: allow to match $HOME/.vim/ and $HOME/.config/vim for &viewdir
          (John M Devin)

closes: #15639

Signed-off-by: John M Devin <john.m.devin@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/setup.vim b/src/testdir/setup.vim
index 0e5088a..485675a 100644
--- a/src/testdir/setup.vim
+++ b/src/testdir/setup.vim
@@ -34,6 +34,10 @@
   " defaults before we get here, and test_mksession checks that.
   let $ORIGHOME = $HOME
 
+  if !exists('$XDG_CONFIG_HOME')
+    let $XDG_CONFIG_HOME = $HOME .. '/.config'
+  endif
+
   " Make sure $HOME does not get read or written.
   " It must exist, gnome tries to create $HOME/.gnome2
   let $HOME = getcwd() . '/XfakeHOME'
diff --git a/src/testdir/test_mksession.vim b/src/testdir/test_mksession.vim
index 914d1e3..d0ee6e8 100644
--- a/src/testdir/test_mksession.vim
+++ b/src/testdir/test_mksession.vim
@@ -1270,7 +1270,10 @@
     " use escape() to handle backslash path separators
     call assert_match('^' .. escape($ORIGHOME, '\') .. '/vimfiles', &viewdir)
   elseif has('unix')
-    call assert_match('^' .. $ORIGHOME .. '/.vim', &viewdir)
+    call assert_match(
+          \ '^' .. $ORIGHOME .. '/.vim\|' ..
+          \ '^' .. $XDG_CONFIG_HOME .. '/vim'
+          \ , &viewdir)
   elseif has('amiga')
     call assert_match('^home:vimfiles', &viewdir)
   elseif has('mac')
diff --git a/src/version.c b/src/version.c
index 5c3c5ef..eb88b0d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    721,
+/**/
     720,
 /**/
     719,