Add Copilot auto-fix workflow for dependabot PRs

[Copilot]

Dependabot PRs that break tests or land with merge conflicts require manual intervention. This workflow automates prompting GitHub Copilot to handle both cases.

What's added

.github/workflows/copilot-auto-fix.yml — two jobs:

• fix-failing-tests — fires on workflow_run completion (Build, failure) for any dependabot/* branch. Resolves the associated open PR, deduplicates by scanning existing comments for the run ID, then posts a @copilot comment with repo-specific guidance:

  • Baseline regeneration (dotnet test -- --filter TestCategory=Baseline --test-parameter SetBaseLine=true)
  • Unit/integration test failure triage
  • npm/TypeScript compatibility checks for vscode-bicep / vscode-bicep-ui

• fix-merge-conflicts — fires on pull_request events from dependabot[bot]. Polls mergeStateStatus (10 s intervals, up to ~100 s) until GitHub resolves mergeability, then posts a @copilot comment on DIRTY PRs asking it to resolve conflicts while preserving dependabot's version bumps. Deduplicates to avoid repeat comments on re-sync.

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 28270038837)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 28270038837

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 28270038837"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 28270038837

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 28270038837"

[majastrz]

Can we point this part to a script? One of these two will do it:

• https://github.com/Azure/bicep/blob/main/scripts/UpdateBaselines.ps1
• https://github.com/Azure/bicep/blob/main/scripts/update_baselines.sh

This way if the command changes (due to test framework shenanigans or anything else really), this will continue working.