patch 8.2.1301: Vim9: varargs argument type not parsed properly

Problem:    Vim9: varargs argument type not parsed properly.
Solution:   Skip over the "...". (issue #6507)
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 1354a38..31e7612 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -1956,6 +1956,8 @@
 	    {
 		char_u *sp = p;
 
+		if (STRNCMP(p, "...", 3) == 0)
+		    p += 3;
 		p = skip_type(p, TRUE);
 		if (p == sp)
 		    return p;  // syntax error