Remove periods from list in about-billing-for-github-codespaces#storage-costs-for-prebuilds

[Yewzir]

Closes: #34675

• I have reviewed my changes in staging, available via the View deployment link in this PR's timeline (this link will be available after opening the PR).

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

[github-actions]

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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

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Source	Preview	Production	What Changed
billing/managing-billing-for-github-codespaces/about-billing-for-github-codespaces.md	fpt ghec	fpt ghec

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

[subatoi]

Thanks once again! I'll merge this, too

[github-actions]

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