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.

src/testdir/test_matchadd_conceal.vim

@@ -298,12 +298,14 @@ func Test_cursor_column_in_concealed_line_after_window_scroll()
   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 @@ func Test_cursor_column_in_concealed_line_after_leftcol_change()
   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])

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2405,
 /**/
     2404,
 /**/