Update bollard requirement from 0.15 to 0.16

Updates the requirements on [bollard](https://github.com/fussybeaver/bollard) to permit the latest version.
- [Release notes](https://github.com/fussybeaver/bollard/releases)
- [Commits](fussybeaver/bollard@v0.15.0...v0.16.0)

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

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

Cargo.toml

@@ -28,7 +28,7 @@ edition = "2021"
 
 [dev-dependencies]
 again = "0.1"
-bollard = "0.15"
+bollard = "0.16"
 futures = "0.3"
-tokio = { version = "1", features = ["macros", "time"] }
+tokio = { version = "1", features = ["macros", "time", "rt-multi-thread"] }
 speculoos = "0.11.0"