docs: add validation failure note to GitLab comment strategy

[EsteeCohen]

📝 Description of the Change

The GitLab documentation explained how to disable status comments using
comment_strategy: "disable_all", but did not mention that validation failure
comments are always posted regardless of this setting. This note already exists
for GitHub but was missing from the GitLab section.

This PR adds a callout to the GitLab provider documentation clarifying that
comment_strategy only applies to PipelineRun status comments, and that comments
about errors validating PipelineRuns in the .tekton/ directory are always
posted even when comment_strategy is set to disable_all.

🔗 Linked GitHub Issue

Fixes #
Fixes #2269

🧪 Testing Strategy

• Not Applicable

🤖 AI Assistance

• I have not used any AI assistance for this PR.

✅ Submitter Checklist

• [x ] 📝 My commit messages are clear, informative, and follow the project's How to write a git commit message guide. The Gitlint linter ensures in CI it's properly validated
• [x ] ✨ I have ensured my commit message prefix (e.g., fix:, feat:) matches the "Type of Change" I selected above.
• ♽ I have run make test and make lint locally to check for and fix any
  issues. For an efficient workflow, I have considered installing
  pre-commit and running pre-commit install to
  automate these checks.
• [x ] 📖 I have added or updated documentation for any user-facing changes.
• 🧪 I have added sufficient unit tests for my code changes.
• 🎁 I have added end-to-end tests where feasible. See README for more details.
• 🔎 I have addressed any CI test flakiness or provided a clear reason to bypass it.
• If adding a provider feature, I have filled in the following and updated the provider documentation:
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[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: EsteeCohen / name: Estee Cohen (b89991f)

[gemini-code-assist]

Code Review

This pull request updates the GitLab provider documentation to clarify the behavior of the comment_strategy setting. Specifically, it adds an informational callout explaining that comment_strategy only applies to PipelineRun status comments, whereas validation errors in the .tekton/ directory are always posted. There are no review comments, and I have no feedback to provide.

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[theakshaypant]

Thank you @EsteeCohen for taking care of this!

[chmouel]

Thanks for the contribution! While i don't think this isn't just a GitLab issue, we don't have it documented elsewhere, so it's good to add.

Is there a way to integrate this as regular text in the documentation part of a sentence instead of a callout? The reason behind is that we (as contributor) naturally tend to use callouts for every specific documentation fix, the documentation becomes fragmented and harder to read as a proper guide.

[EsteeCohen]

@chmouel yes no problem, this makes sense :)
I’ll take care of that