docs: Fix deprecation message for span data/attributes

[mydea]

This was apparently left over from some in-between state, users should actually use spanToJSON(span) there to get attributes.

Backporting this (#10604 ) to v7!

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	78.33 KB (+0.32% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	69.57 KB (+0.41% 🔺)
@sentry/browser (incl. Tracing, Replay with Canvas) - Webpack (gzipped)	73.49 KB (+0.37% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	63.17 KB (+0.39% 🔺)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	33.52 KB (+0.76% 🔺)
@sentry/browser (incl. browserTracingIntegration) - Webpack (gzipped)	33.39 KB (+0.77% 🔺)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	31.37 KB (+0.69% 🔺)
@sentry/browser (incl. sendFeedback) - Webpack (gzipped)	31.37 KB (+0.72% 🔺)
@sentry/browser - Webpack (gzipped)	22.63 KB (+1.04% 🔺)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	76.36 KB (+0.4% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	67.9 KB (+0.46% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	33.66 KB (+0.88% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	24.73 KB (+1.12% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	214.07 KB (+0.41% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	101.87 KB (+0.84% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	74.26 KB (+1.14% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	36.8 KB (+0.71% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	69.93 KB (+0.36% 🔺)
@sentry/react - Webpack (gzipped)	22.67 KB (+0.96% 🔺)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	87.54 KB (+0.14% 🔺)
@sentry/nextjs Client - Webpack (gzipped)	51.72 KB (+2.73% 🔺)
@sentry-internal/feedback - Webpack (gzipped)	17.22 KB (+0.58% 🔺)