build: Updating mediawiki/phan-taint-check-plugin to 1.4.0

And updating CoC link to use Special:MyLanguage (T202047).

Change-Id: I75c260e6ad25fe3d7db9dc8abe21177e3a5782c4

CODE_OF_CONDUCT.md

@@ -1 +1 @@
-The development of this software is covered by a [Code of Conduct](https://www.mediawiki.org/wiki/Code_of_Conduct).
+The development of this software is covered by a [Code of Conduct](https://www.mediawiki.org/wiki/Special:MyLanguage/Code_of_Conduct).

composer.json

@@ -18,6 +18,6 @@
 		]
 	},
 	"extra": {
-		"phan-taint-check-plugin": "1.3.0"
+		"phan-taint-check-plugin": "1.4.0"
 	}
 }