feat: add 'area: testing' label to setup data (#120)

Author: JoshuaKGoldberg

script/labels.json

@@ -9,6 +9,11 @@
 		"description": "Improvements or additions to docs",
 		"name": "area: documentation"
 	},
+	{
+		"color": "6009D7",
+		"description": "Improving how the repository's tests are run and/or code is tested",
+		"name": "area: testing"
+	},
 	{
 		"color": "f9d0c4",
 		"description": "Managing the repository's maintenance",