Single result endpoint does not return correctly populated sensitivity

[sarayourfriend]

Description

The single results endpoint does not populate unstable__sensitivity. This prevents the frontend from blurring sensitive results loaded from direct links.

Reproduction is easy on production. I don't share direct links because I am using results that are designated with sensitive textual content in production (though I believe this example to be a false positive). It is possible to reproduce locally using the testing sensitive terms present locally (running, water, and birds). Just choose a result that is designated to have sensitive text by the testing terms and load it's single result. It will not have the sensitive textual content designation in unstable__sensitivity.

Reproduction

1. Search `api.openverse.engineering/v1/audio/` with `?q=Sofia's Dawn Chorus&unstable__include_sensitive_results=true`. This returns just one result titled "Sofia's Dawn Chorus" that is designated as having sensitive textual content. Verify this in the `unstable__sensitivity` array on the result in the results list.
2. Visit the detail url for that result, UUID `06ea8f9b-68b0-4ffd-939b-cb020ad70b0e`.
3. `unstable__sensitivity` will be an empty array.

Additional context

Marked high because it prevents the frontend's sensitivity feature roll out. cc @dhruvkb as a heads up to the project lead.