Bug report

When trying to use(decode) any png image with the prebuilt vips windows binary it outputs
im_png2vips: no PNG support in your libvips
While a dll is available in the same folder for both libpng and libspng

To Reproduce
Steps to reproduce the behavior:

1. Attempt to decode any png image
2. See Error im_png2vips: no PNG support in your libvips

Screenshots

Environment

• OS: Windows 10
• Vips: 8.10.6 (vips-dev-w64-all-8.10.6)