Fix Code.astro shiki css class replace logic

[giuseppelt]

Changes

The replace uses a regex witch matches anything extra and adds it back to the css class.

Closes #5828

Testing

As mentioned in the linked issue #5828, the actual pinned shiki version v0.11 does work. The v0.12 causes the bug, as a new feature shikijs/shiki#376 adds an extra css class, making the actual logic to fail.

There's a test already in place

astro/packages/astro/test/astro-component-code.test.js

Lines 37 to 41 in 4b16e9e

	it('<Code theme="...">', async () => {
	let html = await fixture.readFile('/custom-theme/index.html');
	const $ = cheerio.load(html);
	expect($('pre')).to.have.lengthOf(1);
	expect($('pre').attr('class')).to.equal('astro-code');

and it will fail when shiki gets updated to v0.12. This PR resolves the issue.

Docs

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[bluwy]

Thanks for the fix!