patch 9.1.1523: tests: test_clipmethod fails in non X11 environment

Problem:  tests: test_clipmethod fails in non X11 environment
Solution: test that $DISPLAY is available

related: #17677

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_clipmethod.vim b/src/testdir/test_clipmethod.vim
index 7573ce2..591b3a2 100644
--- a/src/testdir/test_clipmethod.vim
+++ b/src/testdir/test_clipmethod.vim
@@ -34,7 +34,9 @@
   :wlrestore 1239
   clipreset
 
-  call assert_equal("x11", v:clipmethod)
+  if exists("$DISPLAY")
+    call assert_equal("x11", v:clipmethod)
+  endif
 
   :xrestore 1239
   clipreset
@@ -49,9 +51,11 @@
   call assert_equal("wayland", v:clipmethod)
   call assert_equal(1, has('clipboard_working'))
 
-  set cpm=x11
+  if exists("$DISPLAY")
+    set cpm=x11
 
-  call assert_equal("x11", v:clipmethod)
+    call assert_equal("x11", v:clipmethod)
+  endif
 
   set cpm=wayland
 
@@ -101,7 +105,9 @@
   wlrestore!
 
   call assert_equal("", v:wayland_display)
-  call assert_equal("x11", v:clipmethod)
+  if exists("$DISPLAY")
+    call assert_equal("x11", v:clipmethod)
+  endif
 
   " Do the same but kill a X11 server
 
@@ -150,20 +156,23 @@
   let l:job = job_start(l:cmd, { 'stoponexit': 'kill', 'out_io': 'null'})
 
   call WaitForAssert({-> assert_equal("run", job_status(l:job))})
-  call WaitForAssert({-> assert_match(l:name, serverlist())})
+  if exists("$DISPLAY")
+    call WaitForAssert({-> assert_match(l:name, serverlist())})
+  endif
 
   " Change x server to the one that will be killed, then block until
   " v:clipmethod is none.
-  call remote_send(l:name, ":xrestore " .. l:xdisplay ..
+  if exists("$DISPLAY")
+    call remote_send(l:name, ":xrestore " .. l:xdisplay ..
         \ ' | call DoIt()' .. "\<CR>")
 
-  call EndXServer(l:xdisplay)
+    call EndXServer(l:xdisplay)
+    call WaitFor({-> filereadable('Xtest')})
 
-  call WaitFor({-> filereadable('Xtest')})
-
-  " For some reason readfile sometimes returns an empty list despite the file
-  " existing, this why WaitForAssert() is used.
-  call WaitForAssert({-> assert_equal(['SUCCESS'], readfile('Xtest'))}, 1000)
+    " For some reason readfile sometimes returns an empty list despite the file
+    " existing, this why WaitForAssert() is used.
+    call WaitForAssert({-> assert_equal(['SUCCESS'], readfile('Xtest'))}, 1000)
+  endif
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index ba10341..0ae7983 100644
--- a/src/version.c
+++ b/src/version.c
@@ -720,6 +720,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1523,
+/**/
     1522,
 /**/
     1521,