Update testcontainers requirement from 0.14.0 to 0.15.0

Updates the requirements on [testcontainers](https://github.com/testcontainers/testcontainers-rs) to permit the latest version.
- [Release notes](https://github.com/testcontainers/testcontainers-rs/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-rs/blob/dev/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-rs@0.14.0...0.15)

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

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

Cargo.toml

@@ -18,5 +18,5 @@ url = { version = "2.4.1", features = ["serde"] }
 [dev-dependencies]
 fluent-asserter = "0.1.9"
 mockito = "1.2.0"
-testcontainers = "0.14.0"
+testcontainers = "0.15.0"
 assert-json-diff = "2.0.2"