[Bug]: Phantom `default` changes prevent gateway in-place update

[jvstme]

Steps to reproduce

1. Have no default gateway in the project.
2. Apply the configuration:

type: gateway
name: test-gateway
backend: aws
region: eu-west-1
domain: old.example.com

3. Apply the configuration:

type: gateway
name: test-gateway
backend: aws
region: eu-west-1
domain: new.example.com

Actual behaviour

$ dstack apply -f test.dstack.yml
Found gateway test-gateway. Detected changes that cannot be updated in-place:
- default
- domain

Re-create the gateway? [y/n]:

Expected behaviour

$ dstack apply -f test.dstack.yml
Found gateway test-gateway. Detected changes that can be updated in-place:
- domain

Update the gateway? [y/n]:

dstack version

0.21.0

Server logs

Additional information

On step 2, the gateway is automatically set as the default. On step 3, the client sends default: false, which results in a phantom change being detected.