Use a single .gitignore file

[mokagio]

Follow up on @kean 's comment here: #23996 (comment)

[wpmobilebot]

📲 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	pr24087-dce1c66
	Version	25.7.1
	Bundle ID	org.wordpress.alpha
	Commit	dce1c66
	App Center Build	WPiOS - One-Offs #11512

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[wpmobilebot]

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

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr24087-dce1c66
	Version	25.7.1
	Bundle ID	com.jetpack.alpha
	Commit	dce1c66
	App Center Build	jetpack-installable-builds #10543

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[crazytonyli]

Hey @mokagio, this PR may need a rebase.

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 25.8. This milestone is due in less than 4 days. Please make sure to get it merged by then or assign it to a milestone with a later deadline.

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[mokagio]

Hey @mokagio, this PR may need a rebase.

Thanks @crazytonyli . It should be all done now.