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
diff --git a/src/testdir/dumps/Test_terminal_02.dump b/src/testdir/dumps/Test_terminal_02.dump
index 495d2d2..b9dfdbe 100644
--- a/src/testdir/dumps/Test_terminal_02.dump
+++ b/src/testdir/dumps/Test_terminal_02.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|1|,|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|0|,|1| @10|B|o|t
 | +0#0000000#ffffff0@74
 |~+0#4040ff13&| @73
 |~| @73
diff --git a/src/testdir/dumps/Test_terminal_03.dump b/src/testdir/dumps/Test_terminal_03.dump
index a2883f6..6bc6ee7 100644
--- a/src/testdir/dumps/Test_terminal_03.dump
+++ b/src/testdir/dumps/Test_terminal_03.dump
@@ -7,7 +7,7 @@
 |4|9| @72
 |o|n|e| |m|o|r|e| |l|i|n|e| @61
 > @74
-|!+2#ffffff16#00e0003|/|b|i|n|/|t|c|s|h| |[|r|u|n@1|i|n|g|]| @36|4@1|,|1| @10|B|o|t
+|!+2#ffffff16#00e0003|/|b|i|n|/|t|c|s|h| |[|r|u|n@1|i|n|g|]| @36|4|3|,|1| @10|B|o|t
 | +0#0000000#ffffff0@74
 |~+0#4040ff13&| @73
 |~| @73