adk deploy app-engine with --validate-agent-import parameter fails because .env files are not included.

[slilichenko]

An agent that runs correctly using adk web and relies on some parameters to be provided via .env file fails if that flag is enabled.

Steps to Reproduce:
Please provide a numbered list of steps to reproduce the behavior:

1. Create a settings class which extends BaseSettings and add an attribute which is not initialized
2. Add .env file which provides the value of the attribute
3. Run adk web to confirm that the agent running
4. Run adk deploy --validate-agent-import and see that the validation fails with pydantic_core._pydantic_core.ValidationError.

• ADK Library Version (pip show google-adk): 1.26.0
• Desktop OS: Mac
• Python Version (python -V): 3.14