Update datastore grpc version

Author: cindy-peng

.readme-partials.yaml

@@ -129,7 +129,7 @@ custom_content: |
   <dependency>
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-datastore</artifactId>
-    <version>2.20.0-grpc-experimental-1-SNAPSHOT</version>
+    <version>2.22.0-grpc-experimental-1-SNAPSHOT</version>
   </dependency>
   ```
   

README.md

@@ -229,7 +229,7 @@ mvn clean install -DskipTests=true
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-datastore</artifactId>
-  <version>2.20.0-grpc-experimental-1-SNAPSHOT</version>
+  <version>2.22.0-grpc-experimental-1-SNAPSHOT</version>
 </dependency>
 ```