fix: postCreate.sh doesn't execute without providing execute permission to the script first

[saikatdas0790]

Why:

Closes: #33165

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

I modified the postCreateCommand in the devcontainer.json to also update permissions on the postCreate.sh file to add the execute permission

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Content directory changes

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Source	Preview	Production	What Changed
codespaces/developing-in-a-codespace/rebuilding-the-container-in-a-codespace.md	fpt ghec	fpt ghec

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

[nguyenalex836]

@saikatdas0790 Thanks so much for opening a PR! I'll get this triaged for review ✨