patch 8.1.0922: terminal scrollback test is flaky

Problem:    Terminal scrollback test is flaky.
Solution:   Wait a bit before running the tail command.
diff --git a/src/testdir/dumps/Test_terminal_01.dump b/src/testdir/dumps/Test_terminal_01.dump
index 22dd323..4a0014f 100644
--- a/src/testdir/dumps/Test_terminal_01.dump
+++ b/src/testdir/dumps/Test_terminal_01.dump
@@ -7,7 +7,7 @@
 |4|8| @72
 >4|9| @72
 |~+0#4040ff13&| @73
-|!+2#ffffff16#00e0003|/|b|i|n|/|t|c|s|h| |[|T|e|r|m|i|n|a|l|]| @35|5|2|,|1| @10|B|o|t
+|!+2#ffffff16#00e0003|/|b|i|n|/|t|c|s|h| |[|T|e|r|m|i|n|a|l|]| @35|5|1|,|1| @10|B|o|t
 | +0#0000000#ffffff0@74
 |~+0#4040ff13&| @73
 |~| @73