build(deps-dev): bump testcontainers.version from 1.20.6 to 1.21.0 (#743)

Bumps `testcontainers.version` from 1.20.6 to 1.21.0.

Updates `org.testcontainers:testcontainers` from 1.20.6 to 1.21.0
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.20.6...1.21.0)

Updates `org.testcontainers:kafka` from 1.20.6 to 1.21.0
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.20.6...1.21.0)

---
updated-dependencies:
- dependency-name: org.testcontainers:testcontainers
  dependency-version: 1.21.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
- dependency-name: org.testcontainers:kafka
  dependency-version: 1.21.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

pom.xml

@@ -21,7 +21,7 @@
         <additionalOptions>-Xdoclint:none</additionalOptions>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <protobuf.version>3.25.6</protobuf.version>
-        <testcontainers.version>1.20.6</testcontainers.version>
+        <testcontainers.version>1.21.0</testcontainers.version>
         <kafka-libs.version>7.9.0</kafka-libs.version>
         <docker.platforms>linux/amd64,linux/arm64</docker.platforms>
     </properties>