Fix dotenv settings source problem in handling extra variables with same prefix in name

pydantic_settings/sources.py

@@ -981,7 +981,9 @@ def __call__(self) -> dict[str, Any]:
             env_used = False
             for field_name, field in self.settings_cls.model_fields.items():
                 for _, field_env_name, _ in self._extract_field_info(field, field_name):
-                    if env_name.startswith(field_env_name):
+                    if env_name == field_env_name or (
+                        lenient_issubclass(field.annotation, BaseModel) and env_name.startswith(field_env_name)
+                    ):
                         env_used = True
                         break
             if not env_used:

tests/test_settings.py

@@ -4978,3 +4978,17 @@ def settings_customise_sources(
     env.set('one', '1')
     s = Settings(one=True, two=True)
     assert s.four is True
+
+
+def test_dotenv_extra_allow_similar_fields(tmp_path):
+    p = tmp_path / '.env'
+    p.write_text('POSTGRES_USER=postgres\nPOSTGRES_USER_2=postgres2\nPOSTGRES_NAME=name')
+
+    class Settings(BaseSettings):
+        model_config = SettingsConfigDict(env_file=p, extra='allow')
+
+        POSTGRES_USER: str
+
+    s = Settings()
+    assert s.POSTGRES_USER == 'postgres'
+    assert s.model_dump() == {'POSTGRES_USER': 'postgres', 'postgres_name': 'name', 'postgres_user_2': 'postgres2'}