Correct the 0.6.0 release date

[tvanreenen]

What this fixes

The 0.6.0 release-preparation PR merged on August 22, 2026, but its changelog heading still recorded August 21, when the release notes were drafted. This updates the heading to the actual release date before v0.6.0 is tagged and published.

Why fix it before publishing

The changelog date should identify when users can obtain the release, and the repository's earlier entries follow that convention. Leaving the previous date would make the permanent changelog disagree with the Git tag, GitHub release, and PyPI publication history.

User impact

This is a one-line documentation correction. It does not change package code, version metadata, dependencies, supported runtimes, archive compatibility, or runtime behavior.

Verification

• Confirmed PR Prepare NumPy Vector Store 0.6.0 for release #25 merged on August 22, 2026.
• Confirmed no v0.6.0 tag, GitHub release, or PyPI 0.6.0 publication exists yet.
• git diff --check passes.

Release note

Once this correction is squash merged, the resulting exact main commit can be tagged as v0.6.0 and used to publish the GitHub and PyPI releases.

[tvanreenen]

Deferring this cosmetic date correction to later documentation work; it is not required to publish v0.6.0.