Bump spring.version from 5.3.20 to 5.3.21

Bumps `spring.version` from 5.3.20 to 5.3.21.

Updates `spring-core` from 5.3.20 to 5.3.21
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v5.3.20...v5.3.21)

Updates `spring-context` from 5.3.20 to 5.3.21
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v5.3.20...v5.3.21)

Updates `spring-beans` from 5.3.20 to 5.3.21
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v5.3.20...v5.3.21)

Updates `spring-web` from 5.3.20 to 5.3.21
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v5.3.20...v5.3.21)

Updates `spring-aop` from 5.3.20 to 5.3.21
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v5.3.20...v5.3.21)

Updates `spring-oxm` from 5.3.20 to 5.3.21
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v5.3.20...v5.3.21)

Updates `spring-test` from 5.3.20 to 5.3.21
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v5.3.20...v5.3.21)

Updates `spring-expression` from 5.3.20 to 5.3.21
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](https://github.com/spring-projects/spring-framework/compare/v5.3.20...v5.3.21)

---
updated-dependencies:
- dependency-name: org.springframework:spring-core
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.springframework:spring-context
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.springframework:spring-beans
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.springframework:spring-web
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.springframework:spring-aop
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.springframework:spring-oxm
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.springframework:spring-test
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.springframework:spring-expression
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/pom.xml b/pom.xml
index 9bcbf92..5925942 100644
--- a/pom.xml
+++ b/pom.xml
@@ -254,7 +254,7 @@
 
         <failIfNoTests>false</failIfNoTests>
         <shade.plugin.version>3.3.0</shade.plugin.version>
-        <spring.version>5.3.20</spring.version>
+        <spring.version>5.3.21</spring.version>
         <springws.version>3.1.3</springws.version>
         <exam.version>4.13.5</exam.version>
         <slf4j.version>1.7.36</slf4j.version>