Upgrade Spring version from 5.3.34 to 5.3.39

see also geoserver/geoserver#7845 and geoserver/geoserver#7846 and associated Jira ticket https://osgeo-org.atlassian.net/browse/GEOS-11506

Author: mprins

geowebcache/pom.xml

@@ -54,7 +54,7 @@
     <gt.version>32-SNAPSHOT</gt.version>
     <jts.version>1.19.0</jts.version>
     <jaiext.version>1.1.26</jaiext.version>
-    <spring.version>5.3.34</spring.version>
+    <spring.version>5.3.39</spring.version>
     <spring.security.version>5.7.12</spring.security.version>
     <xstream.version>1.4.20</xstream.version>
     <commons-io.version>2.16.1</commons-io.version>