patch 8.2.0486: Vim9: some code and error messages not tested

Problem:    Vim9: some code and error messages not tested.
Solution:   Add more tests.
diff --git a/src/evalvars.c b/src/evalvars.c
index 0ffff56..35d038d 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -930,7 +930,7 @@
 	    {
 		if (*semicolon == 1)
 		{
-		    emsg(_("Double ; in list of variables"));
+		    emsg(_("E452: Double ; in list of variables"));
 		    return NULL;
 		}
 		*semicolon = 1;