Update Jackson version to 2.21.2 (#712)

Signed-off-by: András Kerekes <akerekes@google.com>

Author: akerekes

formats/json-jackson/pom.xml

@@ -31,7 +31,7 @@
     <packaging>jar</packaging>
 
     <properties>
-        <jackson.version>2.15.2</jackson.version>
+        <jackson.version>2.21.2</jackson.version>
         <module-name>io.cloudevents.formats.jackson</module-name>
     </properties>