build(deps): update indexmap requirement from 1.9 to 2.1 in /css-inline

Updates the requirements on [indexmap](https://github.com/bluss/indexmap) to permit the latest version.
- [Changelog](https://github.com/bluss/indexmap/blob/master/RELEASES.md)
- [Commits](indexmap-rs/indexmap@1.9.0...2.1.0)

---
updated-dependencies:
- dependency-name: indexmap
  dependency-type: direct:production
...

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

css-inline/Cargo.toml

@@ -36,7 +36,7 @@ attohttpc = { version = "0.24", default-features = false, features = [
 ], optional = true }
 url = "2"
 smallvec = "1"
-indexmap = "1.9"
+indexmap = "2.1"
 pico-args = { version = "0.3", optional = true }
 rayon = { version = "1.7", optional = true }
 rustc-hash = "1.1.0"