Bump indexmap from 1.8.2 to 1.9.1 (#99)

Bumps [indexmap](https://github.com/bluss/indexmap) from 1.8.2 to 1.9.1.
- [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/1.8.2...1.9.1)

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

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

progenitor-impl/Cargo.toml

@@ -9,7 +9,7 @@ description = "An OpenAPI client generator - core implementation"
 [dependencies]
 heck = "0.4.0"
 getopts = "0.2"
-indexmap = "1.8"
+indexmap = "1.9"
 openapiv3 = "1.0.0"
 proc-macro2 = "1.0"
 quote = "1.0"