chore: add sanitization test to heatmaps tests

[pauldambra]

so we don't break sanitization of heatmap data

[vercel]

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Name	Status	Preview	Updated (UTC)
posthog-js	✅ Ready (Inspect)	Visit Preview	Jun 20, 2024 0:51am

[github-actions]

Size Change: 0 B

Total Size: 1.01 MB

ℹ️ View Unchanged

Filename	Size
dist/array.full.js	241 kB
dist/array.js	138 kB
dist/es.js	138 kB
dist/exception-autocapture.js	12.2 kB
dist/module.js	139 kB
dist/recorder-v2.js	109 kB
dist/recorder.js	109 kB
dist/surveys-module-previews.js	59.6 kB
dist/surveys.js	61.1 kB
dist/tracing-headers.js	8.26 kB

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