Register the nearest point average to a UO base. The two bases it cou…

…ld have inherited from its template arguments are PP and VPP, and this object is meant to be a UO

Refs idaholab#18536

framework/src/userobject/NearestPointAverage.C

@@ -18,6 +18,10 @@ NearestPointAverage::validParams()
   InputParameters params =
       NearestPointBase<ElementAverageValue, ElementVariableVectorPostprocessor>::validParams();
 
+  // The base type (ElementAverageValue) and the user object type (ElementVariableVPP) are
+  // postprocessor and VPP respectively and this object is meant to be a UO
+  params.set<std::string>("_moose_base") = "UserObject";
+
   params.addClassDescription(
       "Compute element variable averages for nearest-point based subdomains");