Describe the bug
When feeding a schema with a subschema with an $id field, and then referencing that subschema by its full or relative id, datamodel-codegen tries to download said subschema from the internet, resulting in a httpx.ConnectError: [Errno -2] Name or service not known.

To Reproduce

Example schema:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$ref": "https://schemas.example.org/child",
  "$defs": {
    "child": {
      "$id": "https://schemas.example.org/child",
      "type": "string"
    }
  }
}

Used commandline:

$ cat example.json | datamodel-codegen

Expected behavior
No exception is to be thrown.

Version:

• OS: Linux
• Python version: 3.12
• datamodel-code-generator version: 0.25.0