refactor(alpinejs): Fix test execution and correct minor mistakes in test files

[rururux]

Changes

• Renamed the existing test:e2e command to test:e2e:astro
• Added a new test:e2e:alpinejs command
• Updated test:e2e to run both test:e2e:astro and test:e2e:alpinejs
• Added packages/integrations/alpinejs/playwright.config.js (because CI failed without this)
• Fixed minor mistakes in test files
• Change the test assertions to more stable ones

Previously, the test files for integrations/alpinejs were not being run correctly.
The reason is that the alpinejs integration only contains e2e tests, and those files are not picked up by the test:integrations command.
You can see this in the CI logs of an already-merged pull request, searching for "alpinejs" returns only one hit:
https://github.com/withastro/astro/actions/runs/24900093515/job/72915439313

To address this, I added a new test:e2e:alpinejs command that explicitly runs the tests for the alpinejs integration.
I also moved the contents of the existing test:e2e command into test:e2e:astro, and configured test:e2e to run both test:e2e:astro and test:e2e:alpinejs.

I also noticed that test-utils.ts file was still using .js as the file extension when detecting files, and another had an incorrect path to a test fixture, so I went ahead and corrected those as well.

Additionally, I updated the test assertions to use a more reliable approach, as the tests were occasionally showing as flaky in CI.

Testing

Green CI

Docs

N/A, This will not affect users

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Latest commit: 4b39995

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[rururux]

Just a copy of packages/astro/playwright.config.js

[rururux]

I noticed that running test:e2e:alpinejs in CI shows tests as flaky, so in commit 4b39995 I updated the assertion to make the tests pass more reliably.

before:

after: