Update dependencies

• Das Update von com.gorylenko.gradle-git-properties war notwendig in Vorbereitung auf Gradle 7.0:

  Property 'gitProperties' is not annotated with an input or output annotation. This behaviour has been deprecated and is scheduled to be removed in Gradle 7.0. See https://docs.gradle.org/6.5/userguide/more_about_tasks.html#sec:up_to_date_checks for more details.
  Property 'source' is declared without normalization specified. Properties of cacheable work must declare their normalization via @PathSensitive, @Classpath or @CompileClasspath. Defaulting to PathSensitivity.ABSOLUTE. This behaviour has been deprecated and is scheduled to be removed in Gradle 7.0. See https://docs.gradle.org/6.5/userguide/more_about_tasks.html#sec:up_to_date_checks for more details.

• Die zusätzliche Dependency kam mit Spring Boot 2.3, siehe https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-2.3-Release-Notes#validation-starter-no-longer-included-in-web-starters.