Make load more button load more packages

This adds the functionality of the button.

Contributes to issue CURA-8556.

plugins/Marketplace/PackageList.py

@@ -39,6 +39,7 @@ class PackageList(ListModel):
 
         self.request()
 
+    @pyqtSlot()
     def request(self) -> None:
         """
         Make a request for the first paginated page of packages.

plugins/Marketplace/resources/qml/Plugins.qml

@@ -50,6 +50,7 @@ ScrollView
             height: UM.Theme.getSize("card").height
 
             enabled: pluginList.hasMore && !pluginList.isLoading
+            onClicked: pluginList.request()  //Load next page in plug-in list.
 
             background: Rectangle
             {