patch 8.2.3347: check for legacy script is incomplete

Problem:    Check for legacy script is incomplete. (Naohiro Ono)
Solution:   Also check the :legacy modifier.  Use for string concatenation
            with "." and others (issue #8756)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 9640c50..d29a932 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -2951,7 +2951,7 @@
 			    if (ends_excmd2(p, eap->cmd))
 			    {
 				*errormsg =
-				      _(e_vim9cmd_must_be_followed_by_command);
+				      _(e_legacy_must_be_followed_by_command);
 				return FAIL;
 			    }
 			    cmod->cmod_flags |= CMOD_LEGACY;