fix(core): links with target "_blank" should no be checked by the broken link checker

[slorber]

Motivation

Fix #9758

If a link has target="_blank" (or any other external target !== "_self"), that link shouldn't be checked by the broken link checker because it can't trigger a SPA soft navigation, and can only navigate to an external url.

Test Plan

dogfood

Test links

https://deploy-preview-9788--docusaurus-2.netlify.app/tests/pages/markdown-tests-mdx#linking-to-non-spa-page-with-link-component

[netlify]

✅ [V2]

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 79	🟢 98	🟢 100	🟢 100	🟠 89	Report
/docs/installation	🟠 87	🟢 98	🟢 100	🟢 100	🟠 89	Report
/docs/category/getting-started	🟠 75	🟢 100	🟢 100	🟢 90	🟠 89	Report
/blog	🟠 66	🟢 100	🟢 100	🟢 90	🟠 89	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 64	🟢 97	🟢 100	🟢 100	🟠 89	Report
/blog/tags/release	🟠 70	🟢 100	🟢 100	🟠 80	🟠 89	Report
/blog/tags	🟠 76	🟢 100	🟢 100	🟢 90	🟠 89	Report

[github-actions]

Size Change: +36 B (0%)

Total Size: 986 kB

Filename	Size	Change
website/build/assets/js/main.********.js	759 kB	+36 B (0%)

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	75.1 kB
website/build/assets/css/styles.********.css	114 kB
website/build/index.html	37.9 kB

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