chore(ci): Change Lighthouse trigger from pull_request_target to pull_request

[slorber]

Motivation

The recent Nx critical supply chain attack (https://socket.dev/blog/nx-packages-compromised) is due to the usage of pull_request_target: https://x.com/adnanthekhan/status/1958722939534417989

We also use pull_request_target on this action, but:

• this is very risky, and the code below can introduce critical vulnerabilities
• it doesn't even work because we run Lighthouse on our main branch (see Consolidate Lighthouse CI report #9449 (comment)), and checkout out the base branch would introduce the vulnerability

So, I'm moving the event to the much safer pull_request. This:

• fixes the security risk
• fixes the Lighthouse job for internal PRs
• unfortunately, external PRs won't be able to post the GitHub lighthouse comment.

Posting a comment to an external PR should be fixable. If someone wants to improve our workflow, please submit a PR, but I'll only accept the usage of pull_request_target on tiny workflows that doesn't execute any code outside of the Yaml workflow itself.

See also https://github.blog/security/application-security/how-to-secure-your-github-actions-workflows-with-codeql/

Test Plan

CI

[netlify]

✅ [V2]

Name	Link
🔨 Latest commit	e8afdd5
🔍 Latest deploy log	https://app.netlify.com/projects/docusaurus-2/deploys/68b59a8944f6fb00086b364f
😎 Deploy Preview	https://deploy-preview-11393--docusaurus-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	Report
/	🟠 52	🟢 98	🟢 100	🟢 100	Report
/docs/installation	🟠 61	🟢 97	🟢 100	🟢 100	Report
/docs/category/getting-started	🟠 71	🟢 100	🟢 100	🟠 86	Report
/blog	🟠 59	🟢 96	🟢 100	🟠 86	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 58	🟢 92	🟢 100	🟢 100	Report
/blog/tags/release	🟠 61	🟢 96	🟢 100	🟠 86	Report
/blog/tags	🟠 68	🟢 100	🟢 100	🟠 86	Report