Add maven plugin dependency to the build dependency group in the depe…

…ndabot rules

.github/dependabot.yml

@@ -48,6 +48,7 @@ updates:
  - "org.springframework:*"
  # only used for perf tests based on javax:
  - "org.glassfish:javax.el"
+ - "org.codehaus.plexus:plexus-utils"
  ignore:
  - dependency-name: "javax.validation:*"
  - dependency-name: "org.apache.bval:*"