Retain current selection of gpu type choice to avoid it getting lost

When the options for choices is changed (in the relevant phases or organization or because the user has changed) the current selection can easily be lost if it's not included in the options.

app/grandchallenge/algorithms/forms.py

@@ -441,6 +441,7 @@ def job_requirement_properties_from_organizations(self):
     @property
     def selectable_gpu_type_choices(self):
         choices_set = {
+            self.instance.job_requires_gpu_type,
             *get_default_gpu_type_choices(),
             *chain.from_iterable(
                 self.job_requirement_properties_from_phases["gpu_type_choices"]