docs(actions): add workflow run status reference

[happysnaker]

Why:

Closes: #34987

What's being changed (if available, include any code snippets, screenshots, or gifs):

This PR adds a dedicated Actions reference page for workflow run status and conclusion values, matching the approach requested in the issue discussion.

Changes in this PR:

• add content/actions/reference/workflows-and-actions/workflow-run-statuses.md
• add the new page to the Workflows and actions reference landing page
• link the REST workflow runs page to the new reference so readers can understand the status filter values more easily

The new page distinguishes lifecycle status values from final conclusion values, and calls out two common sources of confusion:

• pending is often caused by concurrency limits
• waiting is often caused by deployment protection rules or required reviews

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

[github-actions]

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Table of review links

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The table shows the files in the content directory that were changed in this pull request. This helps you review your changes on a staging server. Changes to the data directory are not included in this table.

Source	Review	Production	What Changed
actions/reference/workflows-and-actions/index.md	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17
New file: actions/reference/workflows-and-actions/workflow-run-statuses.md	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17
rest/actions/workflow-runs.md	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17

Key: fpt: Free, Pro, Team; ghec: GitHub Enterprise Cloud; ghes: GitHub Enterprise Server

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[happysnaker]

This PR follows the direction requested in #34987: a dedicated reference-style article rather than a reusable snippet. I kept the scope small by documenting the workflow run lifecycle values, linking from the REST workflow-runs page, and calling out the two most confusing cases (pending from concurrency and waiting from deployment protection or required review).