GetPngMetadata does not set HasTransparency correctly for palette-based PNGs #2209

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of ImageSharp
• I have verified if the problem exist in both DEBUG and RELEASE mode
• I have searched open and closed issues to ensure it has not already been reported

ImageSharp version

2.1.3

Other ImageSharp packages and versions

None

Environment (Operating system, version and so on)

Windows 10 21H1

.NET Framework version

.NET6

Description

When calling GetPngMetadata on a palette-based PNG with transparency HasTransparency is false when it should be true.

Steps to Reproduce

var imageInfo = Image.Identify("sample.png");
var metadata = imageInfo.Metadata.GetPngMetadata();
var colorType = metadata.ColorType; // PngColorType.Palette
var transparency = metadata.HasTransparency; // should be true but is false

Images

sample.zip