Ensure config file message is only shown once (#28017)

Fixes #27982



## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes

packages/next/build/babel/loader/get-config.ts

@@ -302,6 +302,7 @@ function getCacheKey(cacheCharacteristics: CharacteristicsGermaneToCaching) {
 
 type BabelConfig = any
 const configCache: Map<any, BabelConfig> = new Map()
+const configFiles: Set<string> = new Set()
 
 export default function getConfig(
   this: NextJsLoaderContext,
@@ -346,7 +347,8 @@ export default function getConfig(
     }
   }
 
-  if (loaderOptions.configFile) {
+  if (loaderOptions.configFile && !configFiles.has(loaderOptions.configFile)) {
+    configFiles.add(loaderOptions.configFile)
     Log.info(
       `Using external babel configuration from ${loaderOptions.configFile}`
     )