Fix test error - Save with update_fields did not affect any rows.

Related to #2951

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For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/OWASP-BLT/BLT/issues/2951?shareId=XXXX-XXXX-XXXX-XXXX).

blt/middleware/ip_restrict.py

@@ -150,7 +150,8 @@ def __call__(self, request):
                     ip_record.agent = agent
                     ip_record.count = new_count
                     ip_record.path = request.path
-                    ip_record.save(update_fields=["agent", "count", "path"])
+                    if ip_record.pk:
+                        ip_record.save(update_fields=["agent", "count", "path"])
 
                     # Check if a transaction is already active before starting a new one
                     if not transaction.get_autocommit():