Addon Manager: Show correct buttons when no git

If git and/or GitPython are not installed, the Addon Manager cannot
check to see if there are any available updates. In that case, show
the "Uninstall" and "Update" buttons. If no update is available,
clicking the update button will simply download a new copy of the
addon.

src/Mod/AddonManager/package_details.py

@@ -331,6 +331,11 @@ class PackageDetails(QWidget):
             self.ui.buttonUninstall.show()
             self.ui.buttonUpdate.hide()
             self.ui.buttonCheckForUpdate.hide()
+        elif status == AddonManagerRepo.UpdateStatus.CANNOT_CHECK:
+            self.ui.buttonInstall.hide()
+            self.ui.buttonUninstall.show()
+            self.ui.buttonUpdate.show()
+            self.ui.buttonCheckForUpdate.hide()
 
         required_version = self.requires_newer_freecad()
         if repo.obsolete: