Bump indexmap from 2.5.0 to 2.6.0

Bumps [indexmap](https://github.com/indexmap-rs/indexmap) from 2.5.0 to 2.6.0.
- [Changelog](https://github.com/indexmap-rs/indexmap/blob/master/RELEASES.md)
- [Commits](indexmap-rs/indexmap@2.5.0...2.6.0)

---
updated-dependencies:
- dependency-name: indexmap
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>