patch 8.2.3109: check for $DISPLAY never fails

Problem:    Check for $DISPLAY never fails.
Solution:   Use eval().
diff --git a/src/testdir/check.vim b/src/testdir/check.vim
index 504a192..6d2d564 100644
--- a/src/testdir/check.vim
+++ b/src/testdir/check.vim
@@ -139,7 +139,7 @@
 " Command to Check for an environment variable
 command -nargs=1 CheckEnv call CheckEnv(<f-args>)
 func CheckEnv(name)
-  if empty('$' .. a:name)
+  if empty(eval('$' .. a:name))
     throw 'Skipped: Environment variable ' .. a:name .. ' is not set'
   endif
 endfunc
diff --git a/src/version.c b/src/version.c
index 9b1ac9a..a36ec80 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3109,
+/**/
     3108,
 /**/
     3107,