patch 8.2.0376: nasty callback test fails on some systems

Problem:    Nasty callback test fails on some systems.
Solution:   Increase the sleep time.
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index 8d32cbc..e452e45 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -2453,7 +2453,7 @@
   call OpenTerms()
 
   call term_sendkeys(g:buf0, "exit\<CR>")
-  sleep 50m
+  sleep 100m
   exe g:buf0 .. 'bwipe'
   set hidden&
 endfunc