Bug (sponsors): Default primary contact field to True for first contact

Set the initial `primary` contact value to True in the form, ensuring only the first contact is marked as primary. All additional contact forms added will default to False.
Form validation remains unchanged in the event that the `primary` field is unchecked by the user.

Closes python#2610

sponsors/forms.py

@@ -54,6 +54,10 @@ class Meta:
     max_num=5,
 )
 
+formset = SponsorContactFormSet(
+    initial=[{"primary": True}]
+)
+
 
 class SponsorshipsBenefitsForm(forms.Form):
     """
@@ -285,7 +289,10 @@ def __init__(self, *args, **kwargs):
         if self.data:
             self.contacts_formset = SponsorContactFormSet(self.data, **formset_kwargs)
         else:
-            self.contacts_formset = SponsorContactFormSet(**formset_kwargs)
+            self.contacts_formset = SponsorContactFormSet(
+                initial=[{"primary": True}],
+                **formset_kwargs
+            )
 
     def clean(self):
         cleaned_data = super().clean()

sponsors/tests/test_forms.py

@@ -534,6 +534,15 @@ def test_invalidate_form_if_no_primary_contact(self):
         msg = "You have to mark at least one contact as the primary one."
         self.assertIn(msg, form.errors["__all__"])
 
+    def test_initial_primary_contact(self):
+        form = SponsorshipApplicationForm()
+        formset = form.contacts_formset
+
+        self.assertTrue(
+            formset.forms[0].initial.get("primary"),
+            "The primary field in the first contact form should be initially set to True."
+        )
+
 
 class SponsorContactFormSetTests(TestCase):
     def setUp(self):