[UI Tests] - Fix failing testCreateScheduledPost test

[jostnes]

Description

This fixes the failing testCreateScheduledPost() in PostTests in iPhone (the issue was also reproducible locally) that happened because the first day in the next month's calendar can't be selected. The fix is adding a condition to ensure that the month has changed before the tap.

Testing

CI should be 🟢 and testCreateScheduledPost() should pass on iPhone

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	Build Number	pr22135-077d381
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	Bundle ID	com.jetpack.alpha
	Commit	077d381
	App Center Build	jetpack-installable-builds #7040

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📲 You can test the changes from this Pull Request in WordPress Alpha by scanning the QR code below to install the corresponding build.

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr22135-077d381
	Version	23.8
	Bundle ID	org.wordpress.alpha
	Commit	077d381
	App Center Build	WPiOS - One-Offs #8017

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[tiagomar]

Thanks for working on this, @jostnes ! 🙇‍♂️

I tested the changes locally and could reproduce the issue after reverting this PRs changes. The only thing I would add is that the issue also impacted iPad.