Update hashbrown to the latest version

[blinxen]

Update hashbrown to version 0.15.4. Should also fix #2046.

[Byron]

Thanks a lot for contributing!

It is awesome to see that no change is necessary to perform the upgrade, I was absolutely convinced that raw APIs are in use that are now forbidden. Probably I just confused this with crates-index-diff though, where the upgrade was indeed more involved.

[EliahKagan]

This updates what gix-hashtable re-exports, so I think it probably does qualify as a breaking change to the gix-hashtable API, even though nothing else in the workspace needed to be adjusted to accommodate it.

@Byron Should something be done to ensure this precipitates an appropriate version bump and generates a changelog entry of the correct type? (Assuming I'm right that this effect is needed, amending the commit to start with change!: would achieve it, but it could be achieved subsequently in other ways.)

Edit: Alternatively, if cargo-smart-release recognizes chore!: then this should be fine at least as far as the automatic version adjustment goes. (I interpret this guide to mean that we would not ordinarily use chore!:, but it may be that this only applies to the non-breaking chore:.)

Edit 2: Since the chore!: prefix was added in the force-push, it looks like this was intentional and should have the right effect. Sorry about the noise. (I can try to open a PR later to update the instructions in DEVELOPMENT.md to clarify that chore! is usable.)

[Byron]

Indeed, chore is discouraged even though I would expect it to work. It just felt so much more fitting, while I didn't remember DEVELOPMENT.md at all 😅.
Maybe it's best to wait for the next release to see if chore! does indeed work, and then DEVELOPMENT.md could be rephrased. Generally, I still wouldn't use chore as these changes aren't interesting for changelogs. But when they are breaking, that's a different matter and maybe that's what's currently missing in DEVELOPMENT.md.