build(deps): update mockall requirement in /flipt-evaluation (#305)

Updates the requirements on [mockall](https://github.com/asomers/mockall) to permit the latest version.
- [Changelog](https://github.com/asomers/mockall/blob/master/CHANGELOG.md)
- [Commits](asomers/mockall@v0.12.1...v0.13.0)

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

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

flipt-evaluation/Cargo.toml

@@ -21,4 +21,4 @@ chrono = { version = "0.4.31", features = ["serde"] }
 web-time = "1.1.0"
 
 [dev-dependencies]
-mockall = "0.12.1"
+mockall = "0.13.0"