Bump doxiaSitetoolsVersion from 2.0.0-M16 to 2.0.0-M18

Bumps `doxiaSitetoolsVersion` from 2.0.0-M16 to 2.0.0-M18.

Updates `org.apache.maven.doxia:doxia-site-model` from 2.0.0-M16 to 2.0.0-M18
- [Release notes](https://github.com/apache/maven-doxia-sitetools/releases)
- [Commits](apache/maven-doxia-sitetools@doxia-sitetools-2.0.0-M16...doxia-sitetools-2.0.0-M18)

Updates `org.apache.maven.doxia:doxia-site-renderer` from 2.0.0-M16 to 2.0.0-M18
- [Release notes](https://github.com/apache/maven-doxia-sitetools/releases)
- [Commits](apache/maven-doxia-sitetools@doxia-sitetools-2.0.0-M16...doxia-sitetools-2.0.0-M18)

Updates `org.apache.maven.doxia:doxia-integration-tools` from 2.0.0-M16 to 2.0.0-M18
- [Release notes](https://github.com/apache/maven-doxia-sitetools/releases)
- [Commits](apache/maven-doxia-sitetools@doxia-sitetools-2.0.0-M16...doxia-sitetools-2.0.0-M18)

---
updated-dependencies:
- dependency-name: org.apache.maven.doxia:doxia-site-model
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.apache.maven.doxia:doxia-site-renderer
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.apache.maven.doxia:doxia-integration-tools
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

pom.xml

@@ -199,7 +199,7 @@ under the License.
     <!-- for dependencies -->
     <jettyVersion>9.4.53.v20231009</jettyVersion>
     <doxiaVersion>2.0.0-M8</doxiaVersion>
-    <doxiaSitetoolsVersion>2.0.0-M16</doxiaSitetoolsVersion>
+    <doxiaSitetoolsVersion>2.0.0-M18</doxiaSitetoolsVersion>
     <wagonVersion>3.5.3</wagonVersion>
     <slf4jVersion>1.7.36</slf4jVersion>
     <!-- for ITs -->