patch 8.2.1573: Vim9: getreg() does not take "true" as argument

Problem:    Vim9: getreg() does not take "true" as argument.
Solution:   Use tv_get_bool_chk().  (closes #6820)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 69f7816..340ecf0 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -3336,9 +3336,9 @@
 	error = strregname == NULL;
 	if (argvars[1].v_type != VAR_UNKNOWN)
 	{
-	    arg2 = (int)tv_get_number_chk(&argvars[1], &error);
+	    arg2 = (int)tv_get_bool_chk(&argvars[1], &error);
 	    if (!error && argvars[2].v_type != VAR_UNKNOWN)
-		return_list = (int)tv_get_number_chk(&argvars[2], &error);
+		return_list = (int)tv_get_bool_chk(&argvars[2], &error);
 	}
     }
     else