Bump org.springframework:spring-framework-bom from 6.1.20 to 6.1.21 (#3958)

Bumps [org.springframework:spring-framework-bom](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](spring-projects/spring-framework@v6.1.20...v6.1.21)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

build.gradle

@@ -70,7 +70,7 @@ ext {
 	springBootVersion = '3.2.12' // docs module
 	springDataVersion = '2024.0.13'
 	springRetryVersion = '2.0.12'
-	springVersion = '6.1.20'
+	springVersion = '6.1.21'
 	zookeeperVersion = '3.8.4'
 
 	idPrefix = 'kafka'