chore(warn): include key name in inject() usage warning

Author: Tia-ani

src/v3/apiInject.ts

@@ -66,6 +66,7 @@ export function inject(
       warn(`injection "${String(key)}" not found.`)
     }
   } else if (__DEV__) {
-    warn(`inject() can only be used inside setup() or functional components.`)
+    const keyName = key ? String(key) : 'unknown'
+    warn(`inject(${keyName}) can only be used inside setup() or functional components.`)
   }
-}
+}