fix(tracing-internal): Avoid classifying protocol-relative URLs as same-origin urls

[Lms24]

Bored at the airport (4h delay) lol

To fix #8099, we need to adjust our tracePropagationTargets default regex to account for protocol-relative URLs. These were previously classified as same-origin, relative URLs, causing tracing headers to be attached which in turn potentially caused CORS errors for users.

closes #8099

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	21.03 KB (+0.03% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	65.63 KB (+0.02% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.57 KB (+0.04% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	58.09 KB (+0.02% 🔺)
@sentry/browser - Webpack (gzipped + minified)	21.17 KB (0%)
@sentry/browser - Webpack (minified)	69.04 KB (0%)
@sentry/react - Webpack (gzipped + minified)	21.19 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	49.12 KB (+0.01% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	28.65 KB (+0.04% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	26.89 KB (+0.04% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	47.7 KB (+0.19% 🔺)
@sentry/replay - Webpack (gzipped + minified)	41.57 KB (+0.25% 🔺)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	66.6 KB (+0.14% 🔺)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	59.48 KB (+0.16% 🔺)

[lforst]

very interesting

[gongpeione]

In my opinion, using /^\/(?!\\/)/ would be more appropriate? since there may be requests like fetch('/') with a very small probability.

[Lms24]

Good catch, thanks @gongpeione!