Bump mavenPluginPluginVersion from 3.12.0 to 3.13.0

Bumps `mavenPluginPluginVersion` from 3.12.0 to 3.13.0.

Updates `org.apache.maven.plugin-tools:maven-plugin-annotations` from 3.12.0 to 3.13.0
- [Release notes](https://github.com/apache/maven-plugin-tools/releases)
- [Commits](https://github.com/apache/maven-plugin-tools/compare/maven-plugin-tools-3.12.0...maven-plugin-tools-3.13.0)

Updates `org.apache.maven.plugins:maven-plugin-plugin` from 3.12.0 to 3.13.0
- [Release notes](https://github.com/apache/maven-plugin-tools/releases)
- [Commits](https://github.com/apache/maven-plugin-tools/compare/maven-plugin-tools-3.12.0...maven-plugin-tools-3.13.0)

---
updated-dependencies:
- dependency-name: org.apache.maven.plugin-tools:maven-plugin-annotations
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.apache.maven.plugins:maven-plugin-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/pom.xml b/pom.xml
index d379a70..b2ce0c6 100644
--- a/pom.xml
+++ b/pom.xml
@@ -118,7 +118,7 @@
     <whisker.site.url>file:${whisker.site.local}</whisker.site.url>
     <whisker.site.name>Whisker Website</whisker.site.name>
     <whisker.site.id>org.apache.creadur.whisker.site</whisker.site.id>
-    <mavenPluginPluginVersion>3.12.0</mavenPluginPluginVersion>
+    <mavenPluginPluginVersion>3.13.0</mavenPluginPluginVersion>
     <!-- Cannot upgrade to 3.0.0 because it requires Java 7 -->
     <findbugsPluginVersion>3.0.5</findbugsPluginVersion>
   </properties>