harden: use yaml.safe_load in base_config.py

[dajiaohuang]

Description

Use yaml.safe_load instead of yaml.load with FullLoader in base_config.py for security hardening (gitlab.bandit.B506).

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Security fix

Tests

Basic verification was performed. The change replaces yaml.load(f, Loader=yaml.FullLoader) with yaml.safe_load(f), which is the recommended remediation for bandit B506.

Checklist

• I have signed the Contributor License Agreement (CLA).
• My code follows the coding guidelines of this project.
• I have performed a self-review of my own code.
• My changes generate no new warnings.

Fixes #13652

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