fix(serverless): [v7] Check if cloud event callback is a function

[AbhiPrasad]

Backport of #11701 to v7

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	80.71 KB (+0.17% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	71.68 KB (+0.19% 🔺)
@sentry/browser (incl. Tracing, Replay with Canvas) - Webpack (gzipped)	75.7 KB (+0.19% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	65.31 KB (+0.2% 🔺)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	35.62 KB (+0.37% 🔺)
@sentry/browser (incl. browserTracingIntegration) - Webpack (gzipped)	35.5 KB (+0.38% 🔺)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	31.57 KB (0%)
@sentry/browser (incl. sendFeedback) - Webpack (gzipped)	31.58 KB (0%)
@sentry/browser - Webpack (gzipped)	22.78 KB (0%)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	78.89 KB (+0.16% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	70.25 KB (+0.2% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	36.02 KB (+0.36% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	25.27 KB (0%)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	221.21 KB (+0.23% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	109.01 KB (+0.45% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	75.79 KB (0%)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	39.3 KB (+0.35% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	72.17 KB (+0.2% 🔺)
@sentry/react - Webpack (gzipped)	22.81 KB (0%)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	90 KB (+0.15% 🔺)
@sentry/nextjs Client - Webpack (gzipped)	54.15 KB (+0.26% 🔺)
@sentry-internal/feedback - Webpack (gzipped)	17.32 KB (0%)