[JENKINS-55582] Refinement to at least handle nonstandard $JENKINS_HOME/plugins/$shortName.hpi and warn about $shortName-$version.hpi.

core/src/main/java/hudson/PluginManager.java

@@ -601,7 +601,7 @@ public abstract class PluginManager extends AbstractModelObject implements OnMas
     }
 
     void considerDetachedPlugin(String shortName) {
-        if (new File(rootDir, shortName + ".jpi").isFile()) {
+        if (new File(rootDir, shortName + ".jpi").isFile() || new File(rootDir, shortName + ".hpi").isFile()) {
             LOGGER.fine(() -> "not considering loading a detached dependency " + shortName + " as it is already on disk");
             return;
         }