Fix Unity license forwarding in builder action

[0x5143]

Motivation

• CI jobs failed because organization UNITY_LICENSE secrets are not automatically injected into composite actions or forwarded to game-ci/unity-builder@v4 by name.
• The composite action needs explicit inputs/env passthrough so callers can expose secrets to the inner action.
• The previous masking step ran even when no serial was set, causing noisy or invalid behavior.

Description

• Add inputs unityLicense, unitySerial, unityEmail, and unityPassword to .github/actions/unity-builder/action.yaml so callers can pass Unity credentials.
• Forward these values as environment variables to game-ci/unity-builder@v4 using inputs.* || env.*, and change the masking step to only mask when a serial exists.
• Update README.md example to show unityLicense: ${{ secrets.UNITY_LICENSE }} and document that organization secrets must be exposed from the calling workflow via with inputs or job env.

Testing

• Validated the composite action YAML with ruby -e 'require "yaml"; YAML.load_file(".github/actions/unity-builder/action.yaml")', which succeeded.
• Ran git diff --check to ensure there are no whitespace or diff issues, which succeeded.

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Codex Task