[NO-TICKET] Update ahash to 0.7.8 to fix miri build issue

**What does this PR do?**

This commit updates the `ahash` dependency to version 0.7.8.

**Motivation:**

This version includes tkaitchuck/aHash#201
which fixes miri in CI (and in general any stuff that runs with rust
nightly).

**Additional Notes:**

N/A

**How to test the change?**

Validate that CI is still green.

Author: ivoanjo