protoc 21.7 not found

I originally thought this was a typo, but it seems protoc 21.7 does exist. So, edit:

The [build.gradle snippet in the web tutorial](https://developer.android.com/codelabs/android-proto-datastore#4) specifies:

```
protoc {
artifact = "com.google.protobuf:protoc:21.7"
}
```

But Android Studio can't find protoc 21.7 with the provided repository setting:

```
repositories {
google()
mavenCentral()
}
```
giving the error:

```
> Could not resolve all files for configuration ':app:protobufToolsLocator_protoc'.
> Could not find com.google.protobuf:protoc:21.7.
Searched in the following locations:
- https://dl.google.com/dl/android/maven2/com/google/protobuf/protoc/21.7/protoc-21.7.pom
- https://repo.maven.apache.org/maven2/com/google/protobuf/protoc/21.7/protoc-21.7.pom
Required by:
project :app
```

Changing the protoc stanza to read ```artifact = "com.google.protobuf:protoc:3.21.7"``` (i.e. changing the version from 21.7 to 3.21.7) makes this problem go away.

Apri il tutorial web di Android Proto DataStore nello snippet build.gradle collegato e confronta la versione dell’artefatto protoc con l’errore di risoluzione Maven segnalato. Aggiorna il tutorial in modo che l’artefatto utilizzi la versione risolvibile, quindi verifica che le impostazioni del repository visualizzate e la configurazione Gradle siano coerenti.

Scritto dal modello di indicizzazione a partire dal testo della issue.