Clarify milestone creation and deletion steps

[hyarisara]

Why:

Closes: N/A (no existing issue; this is a small documentation improvement)

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

This PR improves grammatical consistency and clarifies the steps for creating, editing, and deleting milestones in GitHub repositories.

Minor grammar and wording fixes in the milestone instructions.

Clarified that deleting a milestone does not affect associated issues or pull requests.

Updated sentences for technical precision without altering functionality or workflow.

No code changes or screenshots were modified.

Check off the following:

A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In this case, the author has verified the instructions against the GitHub interface.

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

Note: Please update the URL for your staging server or codespace.

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
New file: issues/tracking-your-work-with-issues/creating-and-editing-milestones-for-issues-and-pull-requests.md	fpt ghec ghes@ 3.19 3.18 3.17 3.16 3.15 3.14	fpt ghec ghes@ 3.19 3.18 3.17 3.16 3.15 3.14

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

🤖 This comment is automatically generated.

[Sharra-writes]

@hyarisara Thanks for opening a PR. Open source contributors can't create entirely new articles without coordinating with the docs team. If this is something you think is important enough to warrant an entirely new article, please open an issue so we can discuss it.