Remove default gender value

Signed-off-by: Emmy D'Anello <emmy.danello@animath.fr>

registration/migrations/0015_alter_participantregistration_gender.py

@@ -0,0 +1,22 @@
+# Generated by Django 5.1.5 on 2025-03-27 19:18
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("registration", "0014_participantregistration_country"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="participantregistration",
+            name="gender",
+            field=models.CharField(
+                choices=[("female", "Female"), ("male", "Male"), ("other", "Other")],
+                max_length=6,
+                verbose_name="gender",
+            ),
+        ),
+    ]