Fix error handling for the time func alias

Fixes #8835

tpl/math/init.go

@@ -26,7 +26,7 @@ func init() {
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
-			Context: func(args ...interface{}) interface{} { return ctx },
+			Context: func(args ...interface{}) (interface{}, error) { return ctx, nil },
 		}
 
 		ns.AddMethodMapping(ctx.Add,

tpl/math/init_test.go

@@ -36,5 +36,7 @@ func TestInit(t *testing.T) {
 	}
 
 	c.Assert(found, qt.Equals, true)
-	c.Assert(ns.Context(), hqt.IsSameType, &Namespace{})
+	ctx, err := ns.Context()
+	c.Assert(err, qt.IsNil)
+	c.Assert(ctx, hqt.IsSameType, &Namespace{})
 }