Bump testContainersVersion from 1.19.8 to 1.20.4

Bumps `testContainersVersion` from 1.19.8 to 1.20.4.

Updates `org.testcontainers:junit-jupiter` from 1.19.8 to 1.20.4
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.19.8...1.20.4)

Updates `org.testcontainers:kafka` from 1.19.8 to 1.20.4
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.19.8...1.20.4)

Updates `org.testcontainers:testcontainers` from 1.19.8 to 1.20.4
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.19.8...1.20.4)

---
updated-dependencies:
- dependency-name: org.testcontainers:junit-jupiter
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.testcontainers:kafka
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.testcontainers:testcontainers
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

build.gradle.kts

@@ -78,7 +78,7 @@ subprojects {
         // Update kafka_version in `.github/workflows/build.yml` when updating this version
         set("kafkaVersion", "3.8.1")            // https://mvnrepository.com/artifact/org.apache.kafka
         set("confluentVersion", "7.7.2")        // https://packages.confluent.io/maven/io/confluent/kafka-schema-registry-client
-        set("testContainersVersion", "1.19.8")  // https://mvnrepository.com/artifact/org.testcontainers/testcontainers
+        set("testContainersVersion", "1.20.4")  // https://mvnrepository.com/artifact/org.testcontainers/testcontainers
     }
 
     val kafkaVersionOverride = System.getenv("CREEK_KAFKA_VERSION")