Update PHP dependencies

```
Installing dependencies from lock file (including require-dev)
Package operations: 3 installs, 7 updates, 0 removals
  - Downloading nikic/php-parser (v5.1.0)
  - Downloading phpunit/phpunit (9.6.20)
  - Upgrading squizlabs/php_codesniffer (3.7.2 => 3.8.1): Extracting archive
dealerdirect/phpcodesniffer-composer-installer contains a Composer plugin which is currently not in your allow-plugins config. See https://getcomposer.org/allow-plugins
Do you trust "dealerdirect/phpcodesniffer-composer-installer" to execute code and wish to enable it now? (writes "allow-plugins" to composer.json) [y,n,d,?] y
  - Installing dealerdirect/phpcodesniffer-composer-installer (v1.0.0): Extracting archive
  - Upgrading symfony/polyfill-php80 (v1.29.0 => v1.30.0): Extracting archive
  - Installing phpcsstandards/phpcsutils (1.0.9): Extracting archive
  - Installing phpcsstandards/phpcsextra (1.1.2): Extracting archive
  - Upgrading composer/semver (3.3.2 => 3.4.0): Extracting archive
  - Upgrading mediawiki/mediawiki-codesniffer (v42.0.0 => v43.0.0): Extracting archive
  - Upgrading nikic/php-parser (v5.0.2 => v5.1.0): Extracting archive
  - Upgrading myclabs/deep-copy (1.11.1 => 1.12.0): Extracting archive
  - Upgrading phpunit/phpunit (9.6.16 => 9.6.20): Extracting archive
Generating autoload files
```
Bug: https://phabricator.wikimedia.org/T369065

composer.json

@@ -35,8 +35,8 @@
 	},
 	"require-dev": {
 		"ext-curl": "*",
-		"phpunit/phpunit": "9.6.16",
-		"mediawiki/mediawiki-codesniffer": "42.0.0"
+		"phpunit/phpunit": "9.6.20",
+		"mediawiki/mediawiki-codesniffer": "43.0.0"
 	},
 	"support": {
 		"issues": "https://github.com/wikimedia/language-data/issues",
@@ -57,5 +57,10 @@
 			"phpunit",
 			"@cs"
 		]
+	},
+	"config": {
+		"allow-plugins": {
+			"dealerdirect/phpcodesniffer-composer-installer": true
+		}
 	}
 }