Add Cloudflare Actions build regression coverage

[swaggysnippets]

What changed

• adds a Cloudflare fixture with an Astro Action
• verifies two consecutive builds succeed while reusing the warm Vite dependency cache
• removes the broad three-attempt fixture build retry that masked stale prebundle failures

Why

Astro issue #16933 reported Cloudflare builds failing when src/actions/index.ts was present because dependency optimization could observe a stale prebundle. The runtime startup change in #16961 addressed the production failure; this PR adds deterministic regression coverage so that behavior remains protected and optimizer races fail visibly instead of being hidden by retries.

Validation

• Cloudflare integration build passes
• optimizer-sensitive test subset: 11 passed
• full Cloudflare adapter suite: 263 passed, 1 skipped, 0 failed
• Biome and Prettier checks pass
• lockfile frozen install check passes

[changeset-bot]

⚠️ No Changeset found

Latest commit: 2f511e4

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

Name	Type
astro	Patch
@test/astro-client-only-pkg	Patch
@test/before-hydration	Patch
@test/build-assets	Patch
@test/css-order-dynamic-import	Patch
@test/css-order-import	Patch
@test/css-order-layout	Patch
@test/css-order	Patch
@test/dont-delete-me	Patch
@test/lazy-layout	Patch
@test/multiple-jsx-renderers	Patch
@test/multiple-renderers	Patch
@test/prerender-conflict-dynamic-dynamic	Patch
@test/prerender-conflict-static-dynamic	Patch
@test/react-and-solid	Patch
@test/reexport-astro-containing-client-component	Patch
create-astro	Patch
@test/create-astro-not-empty	Patch
@astrojs/alpinejs	Patch
@astrojs/cloudflare	Patch
@astrojs/markdoc	Patch
@astrojs/mdx	Patch
@test/mdx-images	Patch
@test/mdx-infinite-loop	Patch
@test/mdx-namespace	Patch
@test/mdx-optimize	Patch
@test/mdx-page	Patch
@test/mdx-plus-react-errors	Patch
@test/mdx-plus-react	Patch
@test/mdx-env-variables	Patch
@astrojs/netlify	Patch
image-missing-dimention	Patch
@astrojs/node	Patch
@astrojs/preact	Patch
@astrojs/react	Patch
@fixture/react-19-preloads	Patch
@astrojs/solid-js	Patch
@astrojs/svelte	Patch
@astrojs/vercel	Patch
@astrojs/vue	Patch
astro-language-server-test	Patch
language-server-tests	Patch
@astrojs/markdown-satteri	Patch

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