infra: modify browser-testing dependencies update to agentic-workflows

[DeagleGross]

Previously designed approach is not working well, since there are some bugs with autoassignment of issues to copilot: https://github.com/dotnet/aspnetcore/blob/main/.github/workflows/browsertesting-open-issue.yml.

I have redisigned this workflow to use agentic-workflow, where agent automatically spins up the pipeline and creates a PR.

An example of run is in my fork of aspnetcore:
Run: https://github.com/DeagleGross/aspnetcore/actions/runs/24091160813/job/70277664560

In example PR was not published since packages are already on latest version:

All three packages are already at their latest stable versions:
- **Selenium.WebDriver**: 4.41.0 ✓
- **Selenium.Support**: 4.41.0 ✓
- **Microsoft.Playwright**: 1.58.0 ✓
No changes are needed.
● noop (MCP: safeoutputs) · message: "No action needed: All browser-testing dependencies are alrea……
  └ {"result":"success"}
All packages are already at their latest stable versions — no updates needed:
| Package | Current | Latest |
|---|---|---|
| `Selenium.WebDriver` | 4.41.0 | 4.41.0 ✓ |
| `Selenium.Support` | 4.41.0 | 4.41.0 ✓ |
| `Microsoft.Playwright` | 1.58.0 | 1.58.0 ✓ |

[Copilot]

Pull request overview

This PR replaces the existing issue-based workflow for updating browser-testing dependencies with a new agentic workflow approach using GitHub's gh-aw framework. The previous approach had bugs with auto-assignment to Copilot, so this new implementation uses an AI agent to automatically detect new versions and create pull requests directly.

Changes:

• Removes the old issue-creation workflow that had problems with Copilot auto-assignment
• Introduces an agentic workflow that automatically checks for and updates Selenium and Playwright dependencies monthly
• Configures .gitattributes to properly handle auto-generated workflow lock files

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
.github/workflows/browsertesting-open-issue.yml	Removed - old workflow that created issues for manual dependency updates
.github/workflows/browsertesting-issue-body.md	Removed - issue template for the old workflow
.github/workflows/browsertesting-deps-update.md	Added - new agentic workflow definition that fetches latest NuGet versions and updates dependencies
.github/workflows/browsertesting-deps-update.lock.yml	Added - auto-generated GitHub Actions workflow file from the agentic workflow definition
.github/aw/actions-lock.json	Added - lock file for GitHub Actions versions used in agentic workflows
.gitattributes	Modified - marks .lock.yml files as linguist-generated with merge=ours strategy

[wtgodbe]

This is awesome! We can only merge once COPILOT_GITHUB_TOKEN is available, right?

[DeagleGross]

This is awesome! We can only merge once COPILOT_GITHUB_TOKEN is available, right?

thanks Will, yes, without COPILOT_GITHUB_TOKEN it will fail with auth of the agent. We can still merge assuming it will be fixed throughout the month (workflow is set to run once per month)

[wtgodbe]

Is this ready to go? Also, I wonder if the workflow would be able to trigger a run of https://dev.azure.com/dnceng/internal/_build?definitionId=931&_a=summary after opening the PR. Maybe not, since it's internal - it could at least leave a comment on the PR instructing a human engineer to run that pipeline to get the packages mirrored

[wtgodbe]

markdownlint failure unrelated

[wtgodbe]

Can you update the agent to leave a comment on these PRs telling a dev to kick off https://dev.azure.com/dnceng/internal/_build?definitionId=931&_a=summary?