Bump pmd.version from 7.8.0 to 7.9.0 #505

Job	Run time
Checks on JDK 21 (javac+error-prone)	2m 47s
Checks on JDK 21 (ecj)	1m 5s
Checks on JDK 21 (dependency:analyze)	2m 2s
Checks on JDK 21 (pmd)	2m 41s
Checks on JDK 21 (cpd)	1m 15s
Checks on JDK 21 (spotbugs)	4m 42s
Checks on JDK 21 (checkstyle)	1m 41s
Checks on JDK 21 (javac+lint)	1m 14s
Checks on JDK 21 (javac+lint-all-warnings)	1m 23s
Checks on JDK 21 (check-copyrights)	2m 17s
Checks on JDK 21 (rewrite)	4m 9s
	25m 16s

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