Add unit tests for SettingsForm

[devin-ai-integration]

Add unit tests for SettingsForm

Summary

Added comprehensive unit tests for the SettingsForm class in realworld/accounts/tests.py covering three specific scenarios:

1. All fields filled - Tests form submission with email, name, bio, image, and password all provided
2. Partial fields filled - Tests form submission with some fields empty (bio, image, password)
3. Valid form with uncommitted save - Tests form.save(commit=False) behavior to ensure database isn't updated

The tests follow existing patterns in the codebase and verify both form validation and the resulting user object state, including proper password handling logic.

Review & Testing Checklist for Human

• Verify test scenarios match requirements - Confirm the 3 test cases cover the originally requested scenarios
• Check password handling logic - Ensure empty password field doesn't update user's password (test_partial_fields_filled)
• Run tests locally - Execute python manage.py test realworld.accounts.tests.TestSettingsForm to verify all pass
• Validate field assertions - Check that assertIsNone(updated_user.image) is correct for empty URLField values

Notes

• All existing tests continue to pass (16/16 tests in accounts app)
• Tests use proper Django testing patterns with setUp method and realistic test data
• Fixed URLField behavior: empty strings are stored as None for fields with null=True

Link to Devin run: https://app.devin.ai/sessions/0a399681d0354788ac23f8410a332f8c
Requested by: @jpartovi

[devin-ai-integration]

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