fix upper bound

Signed-off-by: Olivier Lamy <olamy@apache.org>

pom.xml

@@ -53,7 +53,7 @@
     <slf4j.version>1.7.35</slf4j.version>
     <jetty.version>9.4.43.v20210629</jetty.version>
     <ehcache.version>3.9.9</ehcache.version>
-    <spring.version>5.3.20</spring.version>
+    <spring.version>5.3.21</spring.version>
     <openjpa.version>3.1.1</openjpa.version>
     <log4j.version>2.17.1</log4j.version>
     <jackson.version>2.12.2</jackson.version>