Bump spring.version in /icu4j-spring-vaadin
Bump spring.version in /icu4j-spring-vaadin

Bumps `spring.version` from 4.3.6.RELEASE to 5.2.1.RELEASE.

Updates `spring-core` from 4.3.6.RELEASE to 5.2.1.RELEASE
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v4.3.6.RELEASE...v5.2.1.RELEASE)

Updates `spring-context` from 4.3.6.RELEASE to 5.2.1.RELEASE
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v4.3.6.RELEASE...v5.2.1.RELEASE)

Updates `spring-test` from 4.3.6.RELEASE to 5.2.1.RELEASE
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v4.3.6.RELEASE...v5.2.1.RELEASE)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
LZaruba/icu4j-spring-vaadin