Keep newline at the end of identical-files.json

VS Code's JSON formatter removed it automatically. It turns out
that the easiest way to keep it is to use the
`files.insertFinalNewline` setting, which the JSON formatter obeys.

config/identical-files.json

@@ -571,4 +571,4 @@
     "python/ql/lib/semmle/python/security/internal/EncryptionKeySizes.qll",
     "java/ql/lib/semmle/code/java/security/internal/EncryptionKeySizes.qll"
   ]
-}
+}