Bump org.codehaus.plexus:plexus-testing from 1.5.0 to 1.6.0 (#209)

Bumps [org.codehaus.plexus:plexus-testing](https://github.com/codehaus-plexus/plexus-testing) from 1.5.0 to 1.6.0.
- [Release notes](https://github.com/codehaus-plexus/plexus-testing/releases)
- [Commits](codehaus-plexus/plexus-testing@plexus-testing-1.5.0...plexus-testing-1.6.0)

---
updated-dependencies:
- dependency-name: org.codehaus.plexus:plexus-testing
  dependency-version: 1.6.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

maven-plugin-testing-harness/pom.xml

@@ -120,7 +120,7 @@ under the License.
     <dependency>
       <groupId>org.codehaus.plexus</groupId>
       <artifactId>plexus-testing</artifactId>
-      <version>1.5.0</version>
+      <version>1.6.0</version>
       <exclusions>
         <exclusion>
           <!-- we need as optional dependencies -->