ci(docker): clean submodules before update to fix build errors

[DeckerSU]

Added clean submodules step before git submodule update in the build script to ensure submodules are always in a clean state before checkout. This prevents local changes inside sdk (e.g. changed build_config.json from assets transformer) from blocking the update step.

Fixes: #3137

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✨ Finishing touches

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch patch-fix-submodules-update

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[github-actions]

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[smk762]

Good call, thanks