patch 8.1.2405: matchadd_conceal test fails under valgrind

Problem:    matchadd_conceal test fails under valgrind.
Solution:   Use WaitForAssert() and wait a bit longer.
diff --git a/src/testdir/test_matchadd_conceal.vim b/src/testdir/test_matchadd_conceal.vim
index 25bff3d..7c02087 100644
--- a/src/testdir/test_matchadd_conceal.vim
+++ b/src/testdir/test_matchadd_conceal.vim
@@ -298,12 +298,14 @@
   END
   call writefile(lines, 'Xcolesearch')
   let buf = RunVimInTerminal('Xcolesearch', {})
+  call term_wait(buf, 100)
 
   " Jump to something that is beyond the bottom of the window,
   " so there's a scroll down.
   call term_sendkeys(buf, ":so %\<CR>")
+  call term_wait(buf, 100)
   call term_sendkeys(buf, "/expr\<CR>")
-  call term_wait(buf)
+  call term_wait(buf, 100)
 
   " Are the concealed parts of the current line really hidden?
   let cursor_row = term_scrape(buf, '.')->map({_, e -> e.chars})->join('')
@@ -336,7 +338,7 @@
   call term_wait(buf)
 
   " Are the concealed parts of the current line really hidden?
-  call assert_equal('c', term_getline(buf, '.'))
+  call WaitForAssert({-> assert_equal('c', term_getline(buf, '.'))})
 
   " BugFix check: Is the window's cursor column properly updated for conceal?
   call assert_equal(1, term_getcursor(buf)[1])
diff --git a/src/version.c b/src/version.c
index 53b9538..89896e5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -743,6 +743,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2405,
+/**/
     2404,
 /**/
     2403,