Bump the PMD version used by the plugin to 5.6.1

[sschuberth]

This replaces PR #1623.

Context

To benefit from the fix for pmd/pmd#232. This also includes the fix for pmd/pmd#337.

Contributor Checklist

• Review Contribution Guidelines
• Sign Gradle CLA
• Link to Design Spec for changes that affect more than 1 public API (that is, not in an internal package) or updates to > 20 files
• Provide integration tests (under <subproject>/src/integTest) to verify changes from a user perspective
• Provide unit tests (under <subproject>/src/test) to verify logic
• Update User Guide, DSL Reference, and Javadoc for public-facing changes
• Ensure that tests pass locally: ./gradlew quickCheck <impacted-subproject>:check

Gradle Core Team Checklist

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation including proper use of @since and @Incubating annotations for all public APIs
• Recognize contributor in release notes

[sschuberth]

I have verified that

./gradlew codeQuality:integTest --tests org.gradle.api.plugins.quality.PmdPluginAuxclasspathIntegrationTest

passes locally.

[bmuschko]

What was the actual issue that has been fixed? Can you point us to a description of it?

Did you run the tests you mentioned above on Windows?

[sschuberth]

What was the actual issue that has been fixed? Can you point us to a description of it?

The link is in the commit message: pmd/pmd#337

Did you run the tests you mentioned above on Windows?

Yes, because only Windows was affected, as only Windows does not permit to delete unclosed files.

[sschuberth]

@bmuschko Meanwhile PMD 5.6.0 was released, and I've upgraded my PR to it.

[adangel]

@sschuberth Could you please update this PR to PMD 5.6.1 - the original fix (in 5.5.6 and 5.6.0) was unfortunately incomplete and caused another problem. PMD 5.6.1 has the final fix in it (as well es 5.5.7). See pmd/pmd#364 / pmd/pmd@9fae304
Thanks!

[sschuberth]

Done @adangel, thanks for notifying.

[eriwen]

@w25r please don't forget to add this to release notes, thanking the contributor.