Change section header for workflow job permissions

[FaithOmbongi]

Why:

"How permissions are calculated for a workflow job" should be nested under the "permissions" header for consistency.

Closes: N/A

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

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.
• [x ] 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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Source	Review	Production	What Changed
actions/reference/workflows-and-actions/workflow-syntax.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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[Copilot]

Pull request overview

Nests the workflow job permission calculation guidance under the permissions section.

Changes:

• Changes the section heading from H2 to H3.