Bump plugin-util-api from 1.4.0 to 1.6.0

Bumps [plugin-util-api](https://github.com/jenkinsci/plugin-util-api-plugin) from 1.4.0 to 1.6.0.
- [Release notes](https://github.com/jenkinsci/plugin-util-api-plugin/releases)
- [Changelog](https://github.com/jenkinsci/plugin-util-api-plugin/blob/master/CHANGELOG.md)
- [Commits](jenkinsci/plugin-util-api-plugin@v1.4.0...v1.6.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

pom.xml

@@ -31,7 +31,7 @@
     <jquery3-api.version>3.5.1-2</jquery3-api.version>
     <font-awesome-api.version>5.15.1-1</font-awesome-api.version>
     <bootstrap4-api.version>4.5.3-1</bootstrap4-api.version>
-    <plugin-util-api.version>1.4.0</plugin-util-api.version>
+    <plugin-util-api.version>1.6.0</plugin-util-api.version>
 
     <commons.lang.version>3.9</commons.lang.version>
     <jackson2-api.version>2.11.1</jackson2-api.version>