ci: change channel

[ivokub]

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.
Note that in most cases the PR should be against the develop branch.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How has this been tested?

Please describe the tests that you ran or implemented to verify your changes. Provide instructions so we can reproduce.

• Test A
• Test B

How has this been benchmarked?

Please describe the benchmarks that you ran to verify your changes.

• Benchmark A, on Macbook pro M1, 32GB RAM
• Benchmark B, on x86 Intel xxx, 16GB RAM

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I did not modify files generated from templates
• golangci-lint does not output errors locally
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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Note

Low Risk
CI notification routing only; no application or security logic changes, though messages will miss the old channel if the bot lacks access to the new one.

Overview
Updates the reusable Slack Notifications workflow so GitHub Action success and failure posts go to gnark-build instead of team-gnark-build. Message text and block layout are unchanged; only the Slack destination channel ID/name in both jq payloads is updated.

^{Reviewed by Cursor Bugbot for commit dd76c60. Bugbot is set up for automated code reviews on this repo. Configure here.}