fix: class string separator

[pauldambra]

Default join character in JS (it turns out 🤦) is the comma.

So, in the change to handle newlines in class strings the split string was accidentally joined with a comma instead of a space.

Frustratingly easy bug to introduce but at least now has an assertion to protect us in future

I checked old events in the explorer (pre 1.94.0) to see what format the elements string is presented in. So I think this now formats correctly

[github-actions]

Size Change: +12 B (0%)

Total Size: 747 kB

Filename	Size	Change
dist/array.full.js	177 kB	+3 B (0%)
dist/array.js	118 kB	+3 B (0%)
dist/es.js	118 kB	+3 B (0%)
dist/module.js	118 kB	+3 B (0%)

ℹ️ View Unchanged

Filename	Size
dist/exception-autocapture.js	12 kB
dist/recorder-v2.js	104 kB
dist/recorder.js	58.4 kB
dist/surveys.js	41.5 kB

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