Bump tomcat.version from 10.0.20 to 10.0.21

Bumps `tomcat.version` from 10.0.20 to 10.0.21.

Updates `tomcat-tribes` from 10.0.20 to 10.0.21

Updates `tomcat-juli` from 10.0.20 to 10.0.21

---
updated-dependencies:
- dependency-name: org.apache.tomcat:tomcat-tribes
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.apache.tomcat:tomcat-juli
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/modules/clustering/pom.xml b/modules/clustering/pom.xml
index 0477765..ea4bfa5 100644
--- a/modules/clustering/pom.xml
+++ b/modules/clustering/pom.xml
@@ -43,7 +43,7 @@
     </scm>
 
     <properties>
-        <tomcat.version>10.0.20</tomcat.version>
+        <tomcat.version>10.0.21</tomcat.version>
     </properties>
 
     <dependencies>