patch 8.2.3055: strange error for assigning to "x.key" on non-dictionary

Problem:    Strange error for assigning to "x.key" on non-dictionary.
Solution:   Add a specific error message. (closes #8451)
diff --git a/src/errors.h b/src/errors.h
index a4dcea2..00894ef 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -448,3 +448,5 @@
 	INIT(= N_("E1201: Decryption failed: pre-mature end of file!"));
 EXTERN char e_no_white_space_allowed_after_str_str[]
 	INIT(= N_("E1202: No white space allowed after '%s': %s"));
+EXTERN char e_dot_can_only_be_used_on_dictionary_str[]
+	INIT(= N_("E1203: Dot can only be used on a dictionary: %s"));