[Config] Add unused vars for some call sites

The `unused` vars were added to address a warning raised by errorprone
about ignoring returned types.

(internal) See b/424298831

Author: rlazo

firebase-config/src/main/java/com/google/firebase/remoteconfig/internal/ConfigAutoFetch.java

@@ -37,6 +37,7 @@
 import java.util.Random;
 import java.util.Set;
 import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 import org.json.JSONException;
 import org.json.JSONObject;
@@ -248,11 +249,11 @@ private void autoFetch(int remainingAttempts, long targetVersion) {
 
     // Randomize fetch to occur between 0 - 4 seconds.
     int timeTillFetch = random.nextInt(4);
-    scheduledExecutorService.schedule(
+    ScheduledFuture<?> unused = scheduledExecutorService.schedule(
         new Runnable() {
           @Override
           public void run() {
-            fetchLatestConfig(remainingAttempts, targetVersion);
+            Task<Void> unused = fetchLatestConfig(remainingAttempts, targetVersion);
           }
         },
         timeTillFetch,

firebase-config/src/main/java/com/google/firebase/remoteconfig/internal/ConfigRealtimeHttpClient.java

@@ -57,6 +57,7 @@
 import java.util.Random;
 import java.util.Set;
 import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -381,7 +382,7 @@ private synchronized void makeRealtimeHttpConnection(long retryMilliseconds) {
 
     if (httpRetriesRemaining > 0) {
       httpRetriesRemaining--;
-      scheduledExecutorService.schedule(
+      ScheduledFuture<?> unused = scheduledExecutorService.schedule(
           new Runnable() {
             @Override
             public void run() {