patch 8.0.0334: can't access b:changedtick from a dict reference

Problem:    Can't access b:changedtick from a dict reference.
Solution:   Make changedtick a member of the b: dict. (inspired by neovim
            #6112)
diff --git a/src/Makefile b/src/Makefile
index 153e526..52c74f2 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2099,6 +2099,7 @@
 	test_cdo \
 	test_channel \
 	test_charsearch \
+	test_changedtick \
 	test_cmdline \
 	test_command_count \
 	test_crypt \