🐛 (go/v4) fix: revert accidental addition of explicit docker.io registry in Dockerfile

[camilamacedo86]

✅ Why?

Docker already defaults to Docker Hub (docker.io) when no registry is specified.
So both forms are functionally the same, but:

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2. Keeps the scaffold clean and idiomatic

• Most open source projects use the short form (golang:1.24).
• It's easier to read and better for beginners.
• This follows standard Go and Docker community practices.
• Adding docker.io just adds noise to the file.

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3. Avoids lock-in or assumptions

• Hardcoding docker.io can break things in environments with custom or mirrored registries.
• It may confuse users who want to use private registries or CI configs.
• By writing golang:1.24, we let the Docker config decide where to pull from — which is more flexible and future-proof.

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TL;DR
golang:1.24 already pulls from Docker Hub.
Adding docker.io is not needed — and removing it keeps the Dockerfile clean, standard, and portable.
It was added by mistake in the PR: #4585

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[camilamacedo86]

Hi @dongjiang1989

I am pinging you to make you aware.
It was my mistake since I did not review your PR.