Move ReaderPostTests to WordPressData

[kean]

Similar to #25287. I'll need it to convert some RemotePost helpers in the future PRs.

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	31096
	Version	PR #25293
	Bundle ID	org.wordpress.alpha
	Commit	28653a2
	Installation URL	3sv4mhn6328vg

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

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	31096
	Version	PR #25293
	Bundle ID	com.jetpack.alpha
	Commit	28653a2
	Installation URL	3o3mudb0lagc8

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