build(deps-dev): bump org.testcontainers:spock in /src

Bumps [org.testcontainers:spock](https://github.com/testcontainers/testcontainers-java) 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:spock
  dependency-version: 1.21.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

src/refimpl-tests/pom.xml

@@ -82,7 +82,7 @@
     <dependency>
       <groupId>org.testcontainers</groupId>
       <artifactId>spock</artifactId>
-      <version>1.20.6</version>
+      <version>1.21.0</version>
       <scope>test</scope>
     </dependency>
     <!-- Mandatory dependencies for using Spock -->