Image unavailability not communicated to users relying on screen-readers to navigate Openverse frontend

[sarayourfriend]

Description

The default alt text of the image title is still used even if "image not available" is shown (thumbnail/upstream image request error).

As far as I can tell, there is zero context available on this page to inform users relying exclusively on screen readers (or related tech)

Reproduction

1. Visit https://openverse.org/image/2dc93cee-34d6-4b98-a76e-92ebc8d4ae73 (this image is unavailable but still present on Openverse at time of issue creation, if the image is gone or is available again, you may need to find another example to work with)
2. Check the alt text of the image and see that it is still the image title.

Additional context

I am making the image request from the UK, without a VPN, from a temporary location. It may be that the image is unavailable from the UK specifically, and is thus not filtered as dead when the API checks it or this was available at one point and the API is used a cached check leading to it being included despite not being available.

You can find the specific result I linked above (at time of issue creation) on page 3 of a search for "phytoplankton bloom".

This issue just need to address the fact that the alt text (and the page generally, but really specifically the alt text) does not indicate to screen-reader users that the image is not available. I've marked it a high priority a11y fix as such, because it severely impacts the usability and reliability of the Openverse website for someone in this situation and would be very frustrating to experience first hand (especially if a big group of results were unavailable, as is the case with the related images of the one linked above).