tpl: updates cast.ToTruth to fall back to hreflect.IsTruthful

Concession from review, where cast.ToTruth should fall back to behavior
from hreflect.IsTruthful if the cast.ToBool was unsuccessful.

Author: khayyamsaleem

Diff for: tpl/cast/cast.go

@@ -17,6 +17,7 @@ package cast
 import (
 	"html/template"
 
+	"github.com/gohugoio/hugo/common/hreflect"
 	_cast "github.com/spf13/cast"
 )
 
@@ -58,12 +59,7 @@ func (ns *Namespace) ToBool(v any) (bool, error) {
 func (ns *Namespace) ToTruth(v any) (bool, error) {
 	result, err := ns.ToBool(v)
 	if err != nil {
-		switch v {
-		case "", "nil", "null", "undefined", "NaN":
-			return false, nil
-		default:
-			return true, nil
-		}
+		return hreflect.IsTruthful(v), nil
 	}
 	return result, nil
 }

Diff for: tpl/cast/cast_test.go

@@ -194,9 +194,9 @@ func TestToTruth(t *testing.T) {
 		{template.JSStr("6"), true},
 		{t, true},
 		{nil, false},
-		{"null", false},
-		{"undefined", false},
-		{"NaN", false},
+		{"null", true},
+		{"undefined", true},
+		{"NaN", true},
 	} {
 		errMsg := qt.Commentf("[%d] %v", i, test.v)