Bump spring-framework-bom from 5.3.20 to 5.3.21

Bumps [spring-framework-bom](https://github.com/spring-projects/spring-framework) from 5.3.20 to 5.3.21.
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](spring-projects/spring-framework@v5.3.20...v5.3.21)

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

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

pom.xml

@@ -68,7 +68,7 @@
         <!-- dependency versions -->
         <slf4j.version>1.7.36</slf4j.version>
         <log4j.version>2.17.2</log4j.version>
-        <spring.version>5.3.20</spring.version>
+        <spring.version>5.3.21</spring.version>
         <spring-security.version>5.4.10</spring-security.version>
         <spring.boot.version>2.4.13</spring.boot.version>
         <mockito.version>3.8.0</mockito.version>