Add an agent workflow to identify potentially stale `[Ignore]` attributes

The repository contains tests marked with `[Ignore]` that reference GitHub issues or pull requests. These tests may remain disabled after the referenced issue is resolved or pull request is merged.

Add a scheduled agent workflow that:

1. Finds `[Ignore]` attributes containing GitHub issue or pull request URLs.
2. Identifies references to issues closed as completed or pull requests that were merged.
3. Checks whether an open tracking issue already identifies the same test.
4. Files an issue when revalidation is needed, identifying the fully qualified test name, source path, original reference, and why it now appears unblocked.
5. Applies appropriate labels such as `Test Debt` and `cookie` so Issue Monster can assign the work to Copilot.

There should be at most one open tracking issue per ignored test. The workflow should include a stable, machine-readable identifier—such as the source path and fully qualified test name—in each filed issue and use it to detect an existing open issue before creating another.

The resulting coding task should initially remove `[Ignore]` and run the smallest relevant test selection. If the test passes, the PR can simply re-enable it. If it fails for another reason, the tracking issue provides a place to document and address the newly exposed failure.

The discovery workflow should not assume that resolving the original reference means the test now passes. Its responsibility is to identify potentially stale ignores and create actionable tracking issues.

Start by locating existing scheduled workflows, the C# tests using [Ignore], and the repository’s Issue Monster labeling conventions. Define the stable identifier from each ignored test and use it to search open tracking issues before filing one. Done means the workflow finds completed references, creates one actionable issue with the required metadata and labels, and leaves test revalidation to that follow-up task.

Written by the indexing model from the issue text.