chore(deps): update bollard requirement in the bollard group

Updates the requirements on [bollard](https://github.com/fussybeaver/bollard) to permit the latest version.

Updates `bollard` to 0.21.0
- [Release notes](https://github.com/fussybeaver/bollard/releases)
- [Changelog](https://github.com/fussybeaver/bollard/blob/master/RELEASE.md)
- [Commits](fussybeaver/bollard@v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: bollard
  dependency-version: 0.21.0
  dependency-type: direct:production
  dependency-group: bollard
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

testcontainers/Cargo.toml

@@ -17,7 +17,7 @@ rustdoc-args = ["--cfg", "docsrs"]
 
 [dependencies]
 async-trait = { version = "0.1" }
-bollard = { version = "0.20.0", features = ["buildkit_providerless", "time"] }
+bollard = { version = "0.21.0", features = ["buildkit_providerless", "time"] }
 http = "1.1"
 bytes = "1.6.0"
 conquer-once = { version = "0.4", optional = true }