build(deps): bump solana-program-test from 2.1.5 to 2.1.6 (#6)

Bumps [solana-program-test](https://github.com/anza-xyz/agave) from 2.1.5 to 2.1.6.
- [Release notes](https://github.com/anza-xyz/agave/releases)
- [Changelog](https://github.com/anza-xyz/agave/blob/master/CHANGELOG.md)
- [Commits](anza-xyz/agave@v2.1.5...v2.1.6)

---
updated-dependencies:
- dependency-name: solana-program-test
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>