Bump org.springframework.security:spring-security-bom

Bumps [org.springframework.security:spring-security-bom](https://github.com/spring-projects/spring-security) from 6.4.0-RC1 to 6.4.0.
- [Release notes](https://github.com/spring-projects/spring-security/releases)
- [Changelog](https://github.com/spring-projects/spring-security/blob/main/RELEASE.adoc)
- [Commits](https://github.com/spring-projects/spring-security/compare/6.4.0-RC1...6.4.0)

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

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

gradle/libs.versions.toml

@@ -1,6 +1,6 @@
 [versions]
 org-springframework = "6.2.0"
-org-springframework-security = "6.4.0-RC1"
+org-springframework-security = "6.4.0"
 com-fasterxml-jackson = "2.18.1"
 nimbus-jose-jwt = "9.41.2"
 org-bouncycastle = "1.79"