Fix specification for mailing-list in configuring-notifications.md

[mortax]

Why:

The description of mailing-list is erroneous. Git includes a List-Id mail header.

Closes:

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

Updated the table and included an example.

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• I have reviewed my changes in staging, available via the View deployment link in this PR's timeline.

  • For content changes, you will also see an automatically generated comment with links directly to pages you've modified. The comment won't appear if your PR only edits files in the data directory.

• For content changes, I have completed the self-review checklist.

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The table contains an overview of files in the content directory that have been changed in this pull request. It's provided to make it easy to review your changes on the staging site. Please note that changes to the data directory will not show up in this table.

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Content directory changes

You may find it useful to copy this table into the pull request summary. There you can edit it to share links to important articles or changes and to give a high-level overview of how the changes in your pull request support the overall goals of the pull request.

Source	Preview	Production	What Changed
account-and-profile/managing-subscriptions-and-notifications-on-github/setting-up-notifications/configuring-notifications.md	fpt ghec ghes@ 3.11 3.10 3.9 3.8 ghae	fpt ghec ghes@ 3.11 3.10 3.9 3.8 ghae

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fpt: Free, Pro, Team
ghec: GitHub Enterprise Cloud
ghes: GitHub Enterprise Server
ghae: GitHub AE

[nguyenalex836]

@mortax Thanks so much for opening a PR! I'll get this triaged for review ✨

[guntrip]

Thanks so much for this PR, @mortax! ✨ I made one tiny change, just to update the type of placeholders used, and I'll get this merged.

Thanks again for contributing to our docs!

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