Update itertools requirement from 0.10.3 to 0.12.1

Updates the requirements on [itertools](https://github.com/rust-itertools/itertools) to permit the latest version.
- [Changelog](https://github.com/rust-itertools/itertools/blob/master/CHANGELOG.md)
- [Commits](rust-itertools/itertools@v0.10.3...v0.12.1)

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

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

positional/Cargo.toml

@@ -20,7 +20,7 @@ harness = false
 name = "enum"
 
 [dependencies]
-itertools = "0.10.3"
+itertools = "0.12.1"
 pad = "0.1.6"
 positional_derive = {version = "=0.4.1-rc.0", path = "../positional_derive"}
 proc-macro2 = "1.0.39"