Bump testContainersVersion from 1.21.3 to 1.21.4 in /Plan

Bumps `testContainersVersion` from 1.21.3 to 1.21.4.

Updates `org.testcontainers:testcontainers` from 1.21.3 to 1.21.4
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.21.3...1.21.4)

Updates `org.testcontainers:junit-jupiter` from 1.21.3 to 1.21.4
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.21.3...1.21.4)

Updates `org.testcontainers:nginx` from 1.21.3 to 1.21.4
- [Release notes](https://github.com/testcontainers/testcontainers-java/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-java/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-java@1.21.3...1.21.4)

---
updated-dependencies:
- dependency-name: org.testcontainers:testcontainers
  dependency-version: 1.21.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.testcontainers:junit-jupiter
  dependency-version: 1.21.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.testcontainers:nginx
  dependency-version: 1.21.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

Plan/build.gradle

@@ -93,7 +93,7 @@ subprojects {
         junitVersion = "6.0.1"
         mockitoVersion = "5.19.0"
         seleniumVersion = "4.35.0"
-        testContainersVersion = "1.21.3"
+        testContainersVersion = "1.21.4"
         awaitilityVersion = "4.3.0"
         swaggerVersion = "2.2.36"
         guavaVersion = "33.4.8-jre"