Bump indexmap from 1.8.0 to 1.8.1

Bumps [indexmap](https://github.com/bluss/indexmap) from 1.8.0 to 1.8.1.
- [Release notes](https://github.com/bluss/indexmap/releases)
- [Changelog](https://github.com/bluss/indexmap/blob/master/RELEASES.md)
- [Commits](https://github.com/bluss/indexmap/compare/1.8.0...1.8.1)

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

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