fix: update the return type of setWaitTimeout for convience (#1751)

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Fixes #<issue_number_goes_here> ☕️

Author: mutianf

gax-java/gax/clirr-ignored-differences.xml

@@ -7,4 +7,10 @@
     <className>com/google/api/gax/paging/Page</className>
     <method>* stream*(*)</method>
   </difference>
+  <difference>
+    <differenceType>7006</differenceType>
+    <className>com/google/api/gax/rpc/ServerStreamingCallSettings$Builder</className>
+    <method>*setWaitTimeout*</method>
+    <to>com.google.api.gax.rpc.ServerStreamingCallSettings$Builder</to>
+  </difference>
 </differences>

gax-java/gax/src/main/java/com/google/api/gax/rpc/ServerStreamingCallSettings.java

@@ -299,8 +299,9 @@ public Duration getWaitTimeout() {
      * Set the maximum amount of time to wait for the next message from the server. {@link
      * Duration#ZERO} disables the check for abandoned streams.
      */
-    public void setWaitTimeout(@Nonnull Duration waitTimeout) {
+    public Builder<RequestT, ResponseT> setWaitTimeout(@Nonnull Duration waitTimeout) {
       this.waitTimeout = waitTimeout;
+      return this;
     }
 
     @Override