chore: reorder protoc v25.8 release

[jklukas]

The current versions.bzl has v25.4 as the highest release in the v25.x series, but there exist versions up to v25.8. I have an environment where we're pinned this major version and we'd like to match exactly what's being used in other systems.

Well now looking at the final diff I feel silly. This version already existed, it just wasn't sitting next to the v25.4 that I was initially looking at.

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Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: yes
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: no

Test plan

• Manual testing; please provide instructions so we can reproduce: no testing needed? I produced the change via VERSION=v25.8 bash protoc/private/mirror_protoc_release.sh and then formatted and moved it into the proper order.

[jklukas]

Well now looking at the final diff I feel silly. This version already existed, it just wasn't sitting next to the v25.4 that I was initially looking at.