Bump org.springframework:spring-core from 6.1.20 to 6.1.21

Bumps [org.springframework:spring-core](https://github.com/spring-projects/spring-framework) from 6.1.20 to 6.1.21.
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v6.1.20...v6.1.21)

---
updated-dependencies:
- dependency-name: org.springframework:spring-core
  dependency-version: 6.1.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

buildSrc/build.gradle

@@ -96,7 +96,7 @@ dependencies {
     implementation 'org.asciidoctor:asciidoctor-gradle-jvm:3.3.2'
     implementation 'org.hidetake:gradle-ssh-plugin:2.10.1'
     implementation 'org.jfrog.buildinfo:build-info-extractor-gradle:4.26.3'
-    implementation 'org.springframework:spring-core:6.1.20'
+    implementation 'org.springframework:spring-core:6.1.21'
     implementation 'org.sonarsource.scanner.gradle:sonarqube-gradle-plugin:2.7.1'
 
     testImplementation platform('org.junit:junit-bom:5.8.2')