fix ISO8601 formatter to always use the 24h format

[marandaneto]

💡 Motivation and Context

Closes #103

💚 How did you test it?

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

[marandaneto]

@bddq are you able to test from a branch?
the format was HH already and not hh so I believe it could be the default timezone and locale.
I cannot change my emulator to 12h only for some reason, the settings are blocked.

[bddq]

The locale did the trick. It's working as expected on my side with a 12-hour time format.

[github-actions]

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- fix ISO8601 formatter to always use the 24h format ([#106](https://github.com/PostHog/posthog-ios/pull/106))

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