Photons don't really have an anti-matter pair that we can observe afaik because anti-particles have the same mass and spin but opposite charge as their counterpart. Since photons have no charge, a photons anti-matter pair is just another photon. Furthermore, we know that anti-hydrogen has the same spectral lines as hydrogen so their electromagnetic interactions are the same.

Finding that anti-matter has anti-gravity would be world changing, though I'm setting my expectations very low. It would mean that we have access to the kind of exotic matter needed for a practical Alcubierre warp drive and could open up an entirely new field of space time engineering. It's just extremely unlikely, given all we know, that anti-matter has such properties.