fix(browser): Set anonymous crossorigin attribute on report dialog

[lforst]

Ref: getsentry/sentry#49535 (comment)

Since we don't need to authenticate users on the report dialog endpoint we should not send any credentials with the request.

Also prevents COEP blockage: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Embedder-Policy#avoiding_coep_blockage_with_cors

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	21.51 KB (+0.07% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	67.62 KB (+0.04% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.83 KB (+0.07% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	58.93 KB (+0.05% 🔺)
@sentry/browser - Webpack (gzipped + minified)	21.43 KB (+0.01% 🔺)
@sentry/browser - Webpack (minified)	69.87 KB (0%)
@sentry/react - Webpack (gzipped + minified)	21.46 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	49.81 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	29.4 KB (+0.05% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	27.5 KB (+0.06% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	49.34 KB (0%)
@sentry/replay - Webpack (gzipped + minified)	43.11 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	68.84 KB (+0.02% 🔺)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	61.39 KB (+0.03% 🔺)