Bump org.springframework:spring-framework-bom from 6.1.20 to 6.1.21

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](https://github.com/spring-projects/spring-framework/compare/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] <support@github.com>

gradle/libs.versions.toml

@@ -1,5 +1,5 @@
 [versions]
-org-springframework = "6.1.20"
+org-springframework = "6.1.21"
 org-springframework-security = "6.3.9"
 com-fasterxml-jackson = "2.17.3"
 nimbus-jose-jwt = "9.39.3"