patch 8.0.0724: the message for yanking doesn't indicate the register

Problem:    The message for yanking doesn't indicate the register.
Solution:   Show the register name in the "N lines yanked" message. (Lemonboy,
            closes #1803, closes #1809)
diff --git a/src/Makefile b/src/Makefile
index 6c236ca..80265fd 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2227,6 +2227,7 @@
 	test_regex_char_classes \
 	test_regexp_latin \
 	test_regexp_utf8 \
+	test_registers \
 	test_reltime \
 	test_retab \
 	test_ruby \