Add report-green AzDO pipeline so Build Analysis completes on build-excluded PRs

[kotlarmilos]

Problem

PRs that touch only build-excluded paths (.github/*, docs/*, **.md, LICENSE, THIRD-PARTY-NOTICES.TXT) queue no AzDO build, because MachineLearning-CI and MachineLearning-CodeCoverage exclude those paths from PR validation. Build Analysis waits for an AzDO build.completed event that never arrives and stays in_progress indefinitely, blocking merge. Tracked upstream in dotnet/arcade-services#6311.

Fix

Mirrors dotnet/runtime's eng/pipelines/report-green.yml. Adds build/report-green.yml, an AzDO pipeline with the inverse path filter (it triggers only on the paths the main pipelines exclude) and an agentless no-op job (pool: server, Delay@1). It produces a real AzDO build whose build.completed event lets Build Analysis report green.

This is the mechanism Build Analysis actually uses. A GitHub Actions check posting a same-named Build Analysis run does not work, because Build Analysis is driven by the AzDO event, not by a check run.

Required AzDO setup

The YAML alone is inert until the pipeline is registered in dnceng-public:

1. Create a new pipeline pointing at build/report-green.yml (e.g. MachineLearning-Report-Green).
2. Add it to the PR build validation for main/feature/*/release/* so it runs on PRs.

After that, build-excluded PRs trigger report-green, emit build.completed, and Build Analysis goes green automatically. Build Analysis stays a required check.

[Copilot]

Pull request overview

Adds a minimal GitHub Actions workflow to provide an always-completing required check for PRs that only touch .github/*, avoiding indefinite “in_progress” Build Analysis states when AzDO PR validations don’t run.

Changes:

• Introduces a new .github/workflows/pr-gate.yml workflow triggered on pull_request to main, feature/*, and release/*.
• Adds a single pr-gate job that performs a no-op command (echo) and succeeds.

Show a summary per file

File	Description
.github/workflows/pr-gate.yml	Adds a lightweight PR workflow intended to always succeed so branch protection can rely on a stable, always-completing check.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 0

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.59%. Comparing base (548d4d0) to head (6dd98f1).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7623   +/-   ##
=======================================
  Coverage   69.59%   69.59%           
=======================================
  Files        1484     1484           
  Lines      273606   273606           
  Branches    27949    27949           
=======================================
+ Hits       190410   190415    +5     
+ Misses      75832    75829    -3     
+ Partials     7364     7362    -2     

Flag	Coverage Δ
Debug	69.59% <ø> (+<0.01%)	⬆️
production	63.84% <ø> (+<0.01%)	⬆️
test	89.63% <ø> (ø)

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see 3 files with indirect coverage changes

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