codesniffer: Enable and fix Modernize.FunctionCalls.Dirname.Nested …

…sniff (#34218)

The WordPress-Extra ruleset turns this off. Now that we've dropped PHP
5.6, we can turn it on.

Then, of course, we have to fix all the existing instances of the
problem.

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/6941880745

composer.json

@@ -4,7 +4,7 @@
 	"license": "GPL-2.0-or-later",
 	"require": {},
 	"require-dev": {
-		"automattic/jetpack-changelogger": "^4.0.0"
+		"automattic/jetpack-changelogger": "^4.0.1-alpha"
 	},
 	"scripts": {
 		"test-js": [