Update basic-writing-and-formatting-syntax.md

[amitse]

add single tilde ~ as valid strikethrough syntax

Why:

Closes: #36995

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

Accoding to GFM both single tilde ~ and double tilde ~~ are valid strikethrough markers,

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• All CI checks are passing and the changes look good in the review environment.

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Pull Request Overview

This PR updates the basic writing and formatting syntax documentation to note that both double tilde (~~ ~~) and single tilde (~ ~) can be used for strikethrough formatting according to the GFM specification.

• Updated the strikethrough row to include single tilde markup.
• Adjusted the table to reflect that both tilde formats are valid.

Comments suppressed due to low confidence (1)

content/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax.md:39

• [nitpick] The updated table row mentions the single tilde (~ ~) as valid syntax, but the provided code example still only shows the double tilde usage. Consider adding an example using single tilde to illustrate the new functionality.

| Strikethrough | `~~ ~~` or `~ ~` | None | `~~This was mistaken text~~` | ~~This was mistaken text~~ |

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Source	Review	Production	What Changed
get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax.md	fpt ghec ghes@ 3.16 3.15 3.14 3.13 3.12	fpt ghec ghes@ 3.16 3.15 3.14 3.13 3.12

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

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[Sharra-writes]

Thanks so much for opening a PR with this fix! I'll update the branch and get this merged once tests are passing 🍏

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