Add license qualifier section to code search syntax

[PreciselyAlyss]

Added a new section on the license qualifier for filtering repositories based on their license type.

Why:

Better consolidation of search qualifiers into a (more) common documentation page for a better user experience when learning about applying code search for repositories across GitHub.

Closes: #43284

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

Addition of a brief section with a pointer to the licensing a repository article about how to use license qualifiers for code search on GitHub.

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.

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Source	Review	Production	What Changed
search-github/github-code-search/understanding-github-code-search-syntax.md	fpt ghec	fpt ghec

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

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[Copilot]

Pull request overview

Adds documentation for using a license qualifier in the GitHub Code Search syntax reference, helping users filter results by repository license.

Changes:

• Added a new “License qualifier” section with an example query (license:MIT).
• Updated the qualifiers list to include a link to the new section.

[LOve-luST-LOST]

Alice Fosseneuve your so smart

[github-actions]

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