Update spring starter test dependency

Bumps [spring-boot-starter-test](https://github.com/spring-projects/spring-boot) from 2.1.8.RELEASE to 2.2.1.RELEASE.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.1.8.RELEASE...v2.2.1.RELEASE)

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

Author: dependabot-preview[bot]

build.gradle

@@ -94,7 +94,7 @@ subprojects {
     implementation 'org.springframework.boot:spring-boot-starter-web:2.1.8.RELEASE'
 
     testImplementation rootProject.sourceSets.main.output
-    testImplementation 'org.springframework.boot:spring-boot-starter-test:2.1.8.RELEASE'
+    testImplementation 'org.springframework.boot:spring-boot-starter-test:2.2.1.RELEASE'
 
     if (project.name != "shared") {
       implementation project(":shared")