Update PMD BeanMembersShouldSerialize exclusion (#535)

The BeanMembersShouldSerialize rule has been deprecated since PMD version 6.52.0.  It has been replaced with NonSerializableClass (see https://pmd.github.io/pmd/pmd_rules_java_errorprone.html#beanmembersshouldserialize).  Changed exclusion for BeanMembersShouldSerialize in PMD ruleset.xml to NonSerializableClass.

The change will prevent a "Unable to exclude rules [BeanMembersShouldSerialize] from ruleset reference category/java/errorprone.xml; perhaps the rule name is misspelled or the rule doesn't exist anymore?" messages being displayed in the build output.

A number of projects using this template have already made this change (e.g. https://github.com/hmcts/sscs-hearings-api/blob/master/config/pmd/ruleset.xml#L66).

Co-authored-by: Felix Eyetan <peyetan@yahoo.com>

config/pmd/ruleset.xml

@@ -63,7 +63,7 @@
     <exclude name="UncommentedEmptyMethodBody"/>
   </rule>
   <rule ref="category/java/errorprone.xml">
-    <exclude name="BeanMembersShouldSerialize"/>
+    <exclude name="NonSerializableClass"/>
   </rule>
   <rule ref="category/java/multithreading.xml"/>
   <rule ref="category/java/performance.xml"/>