Fix package name case-insensitivity

Prevent newly uploaded packages from having the same name but in a
different case.

django/thunderstore/repository/package_manifest.py

@@ -13,7 +13,11 @@
     PackageVersionField,
     StrictCharField,
 )
-from thunderstore.repository.utils import does_contain_package, has_duplicate_packages
+from thunderstore.repository.utils import (
+    does_contain_package,
+    has_different_case,
+    has_duplicate_packages,
+)
 
 
 class PackageInstallerSerializer(serializers.Serializer):
@@ -96,6 +100,10 @@ def validate(self, data):
             )
         if does_contain_package(result["dependencies"], reference):
             raise ValidationError("Package depending on itself is not allowed")
+        if has_different_case(reference.without_version):
+            raise ValidationError(
+                "A similar package already exists with different capitalization"
+            )
         return result
 
     def update(self, instance, validated_data):

django/thunderstore/repository/package_reference.py

@@ -257,3 +257,15 @@ def exists(self) -> bool:
         :rtype: bool
         """
         return self.queryset.exists()
+
+    @cached_property
+    def exists_in_any_case(self) -> bool:
+        """
+        Check if a package with a name with different capitalization exists in the db
+
+        :return: True if a different case package exists, False otherwise
+        :rtype: bool
+        """
+        return Package.objects.filter(
+            namespace=self.namespace, name__iexact=self.name
+        ).exists()

django/thunderstore/repository/utils.py

@@ -42,6 +42,14 @@ def has_duplicate_packages(packages: List["PackageReference"]) -> bool:
     return False
 
 
+def has_different_case(reference: "PackageReference") -> bool:
+    if reference.exists:
+        return False
+    elif reference.exists_in_any_case:
+        return True
+    return False
+
+
 def unpack_serializer_errors(field, errors, error_dict=None):
     if error_dict is None:
         error_dict = {}