Add explicit NDK version for CI builds

app-sample/build.gradle

@@ -95,6 +95,10 @@ android {
                 signingConfig signingConfigs.config
             }
         }
+    } else {
+        // it seems to be a bug in NDK handling, github fail to build the project withe the:
+        // `com.android.builder.errors.EvalIssueException: No version of NDK matched the requested version 21.0.6113669. Versions available locally: 21.3.6528147`
+        ndkVersion '21.3.6528147'
     }
 }