Update mockall requirement from 0.14 to 0.15 (#62)

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@v0.14.0...v0.15.0)

---
updated-dependencies:
- dependency-name: mockall
  dependency-version: 0.15.0
  dependency-type: direct:production
...

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Author: dependabot[bot]

Cargo.toml

@@ -33,7 +33,7 @@ tracing = "0.1"
 
 [dev-dependencies]
 tokio = { version = "1", features = ["macros"] }
-mockall = "0.14"
+mockall = "0.15"
 httpmock = "0.8"
 rand = "0.10"