patch 8.2.1128: the write message mentions characters, but it's bytes

Problem:    The write message mentions characters, but it's actually bytes.
Solution:   Change "C" to "B" and "characters" to "bytes".
diff --git a/src/testdir/dumps/Test_tselect_1.dump b/src/testdir/dumps/Test_tselect_1.dump
index cdaee45..9090122 100644
--- a/src/testdir/dumps/Test_tselect_1.dump
+++ b/src/testdir/dumps/Test_tselect_1.dump
@@ -7,4 +7,4 @@
 |~| @48
 |~| @48
 |~| @48
-|"+0#0000000&|X|t|e|s|t|.|c|"| |2|L|,| |2|3|C| @14|1|,|1| @10|A|l@1| 
+|"+0#0000000&|X|t|e|s|t|.|c|"| |2|L|,| |2|3|B| @14|1|,|1| @10|A|l@1|