Moved c8 to devDependencies

no issue

- `c8` is only used to check coverage in testing and we don't directly
  use it from within `tpl`, so this can be moved to `devDependencies`

ghost/tpl/package.json

@@ -19,12 +19,12 @@
     "access": "public"
   },
   "devDependencies": {
+    "c8": "^7.7.2",
     "mocha": "9.0.0",
     "should": "13.2.3",
     "sinon": "11.1.1"
   },
   "dependencies": {
-    "c8": "^7.7.2",
     "lodash.template": "^4.5.0"
   }
 }