Fix allowed contexts for reusable workflow secrets/inputs

[matiboux]

Why:

Closes: #40391

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

This updates the allowed contexts for jobs.<job_id>.secrets.<secret_id> and jobs.<job_id>.with.<input_id> in reusable-workflows.md to match the actual behavior and the documentation in contexts.md. This adds strategy, matrix, inputs, and vars to the allowed contexts for these keys, ensuring consistency.

This also renames placeholders in workflow keys in contexts.md to match those used in reusable-workflows.md, replacing <secrets_id> with <secret_id> and <with_id> with <input_id> for consistency.

Please verify that these changes are correct and align with the intended functionality and actual behavior of GitHub Actions.

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• [ ] 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.

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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/contexts.md	fpt ghec ghes@ 3.18 3.17 3.16 3.15 3.14	fpt ghec ghes@ 3.18 3.17 3.16 3.15 3.14
actions/reference/workflows-and-actions/workflow-syntax.md	fpt ghec ghes@ 3.18 3.17 3.16 3.15 3.14	fpt ghec ghes@ 3.18 3.17 3.16 3.15 3.14

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

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[matiboux]

Following new testing, this PR has been updated to consider the allowed expression contexts from contexts.md as the source of truth and resolve inconsistencies accordingly.

[github-actions[bot]]

A stale label has been added to this pull request because it has been open 30 days with no activity. If you think this pull request should remain open, please add a new comment.

[matiboux]

If you think this pull request should remain open, please add a new comment.

Yes, this is still relevant to this day.