chore: Run ts on test files

[robbie-c]

Changes

We're not running typescript type-checking on our test files.

In the past I've found this is pretty mixed but overall positive, on the one hand you make refactoring easier and end up catching problems you might not have caught, but on the other hand your test files end up with more type coercion which is quite noisy.

Here's my attempt at adding it to posthog-js. I created a new tsconfig.json for the test files which is less strict. If I add strict:true to the test tsconfig, there's another 309 errors left to fix - let's define this at out of scope, it's still a huge improvement in type safety without it

Checklist

• Tests for new code (see advice on the tests we use)
• Accounted for the impact of any changes across different browsers
• Accounted for backwards compatibility of any changes (no breaking changes in posthog-js!)

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Name	Status	Preview	Updated (UTC)
posthog-js	✅ Ready (Inspect)	Visit Preview	Aug 15, 2024 4:17pm

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[github-actions]

Size Change: +232 B (+0.02%)

Total Size: 1.17 MB

Filename	Size	Change
dist/array.full.js	333 kB	+58 B (+0.02%)
dist/array.js	154 kB	+58 B (+0.04%)
dist/main.js	155 kB	+58 B (+0.04%)
dist/module.js	154 kB	+58 B (+0.04%)

ℹ️ View Unchanged

Filename	Size
dist/exception-autocapture.js	10.4 kB
dist/recorder-v2.js	110 kB
dist/recorder.js	110 kB
dist/surveys-preview.js	59.8 kB
dist/surveys.js	66 kB
dist/tracing-headers.js	8.26 kB
dist/web-vitals.js	5.79 kB

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[robbie-c]

@Phanatic Can you take a look at this? (separate to this PR)

[benjackwhite]

I think this is totally worth it