Center align header and description for BlankSlate

[lukasoppermann]

Closes https://github.com/github/primer/issues/6066

Changelog

Header and description of BlankSlate are now centered

Before	After

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 6105520

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Patch

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Or, apply the integration-tests: skipped manually label to skip these checks.

[github-actions]

Uh oh! @lukasoppermann, at least one image you shared is missing helpful alt text. Check your pull request body to fix the following violations:

• Images should have meaningful alternative text (alt text) at line 14
• Images should have meaningful alternative text (alt text) at line 14
• Images should have meaningful alternative text (alt text) at line 14
• Images should have meaningful alternative text (alt text) at line 14

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Learn more about alt text at Basic writing and formatting syntax: images on GitHub Docs.

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[Copilot]

Pull request overview

This PR centers the text alignment for the header and description elements in the BlankSlate component by adding text-align: center; to the CSS module. This complements the existing grid-based centering of the container and ensures that text content within these elements is also centered.

• Adds text-align: center; CSS property to .Heading and .Description classes in the BlankSlate component
• Properly documented as a patch release in the changeset file

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/react/src/Blankslate/Blankslate.module.css	Adds text-align: center; to the shared .Heading, .Description CSS rule to center the text content within these elements
.changeset/great-paws-swim.md	Documents this change as a patch release for @primer/react