ref(serverless): Avoid using pushScope

[mydea]

This is the only place I've found where we use pushScope, and since we updated the withScope signature we can rewrite this.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	75.16 KB (-0.04% 🔽)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	66.58 KB (-0.05% 🔽)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	60.18 KB (-0.06% 🔽)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	31.26 KB (-0.06% 🔽)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	29.87 KB (-0.04% 🔽)
@sentry/browser - Webpack (gzipped)	21.56 KB (-0.04% 🔽)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	72.6 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	64.31 KB (-0.05% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	30.57 KB (-0.05% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped)	22.63 KB (-0.08% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	202.28 KB (-0.07% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	92.4 KB (-0.15% 🔽)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	67.45 KB (-0.2% 🔽)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	33.47 KB (-0.06% 🔽)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	66.94 KB (-0.05% 🔽)
@sentry/react - Webpack (gzipped)	21.6 KB (-0.04% 🔽)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	83.72 KB (-0.05% 🔽)
@sentry/nextjs Client - Webpack (gzipped)	48.41 KB (-0.04% 🔽)
@sentry-internal/feedback - Webpack (gzipped)	16.18 KB (0%)