patch 8.0.1716: test for term_setsize() does not give a good error message

Problem:    Test for term_setsize() does not give a good error message.
Solution:   use assert_inrange().
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index 95a131b..6e101cf 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -283,8 +283,7 @@
   let rows = term_getsize(buf)[0]
   call WaitFor({-> term_getline(buf, rows - 1) =~ '149'})
   let lines = line('$')
-  call assert_true(lines <= 100)
-  call assert_true(lines > 90)
+  call assert_inrange(91, 100, lines)
 
   call Stop_shell_in_terminal(buf)
   call term_wait(buf)