[SSHD-1349] On Java 26-ea, PMD 7.17.0 throws StackOverflowError, update

to PMD 7.20.0

- Tested `mvn clean package pmd:check -DskipTetsts'
- Tested OK on Java 17, 21, 25, 26-ea

Author: garydgregory

pom.xml

@@ -117,7 +117,7 @@
         <maven.archiver.version>3.6.5</maven.archiver.version>
         <plexus.archiver.version>4.10.3</plexus.archiver.version>
         <!-- See https://pmd.github.io/ for available latest version -->
-        <pmd.version>7.17.0</pmd.version>
+        <pmd.version>7.20.0</pmd.version>
 
         <sshd.tests.timeout.factor>1.0</sshd.tests.timeout.factor>
         <sshd.tests.rerun.count>2</sshd.tests.rerun.count>