fix: make SessionPoolOptions#setUseMultiplexedSession(boolean) package private (#3136)

Author: rahul2393

google-cloud-spanner/clirr-ignored-differences.xml

@@ -676,4 +676,10 @@
     <method>boolean isEnableExtendedTracing()</method>
   </difference>
 
+  <!-- Multiplexed session enable setter to package private -->
+  <difference>
+    <differenceType>7009</differenceType>
+    <className>com/google/cloud/spanner/SessionPoolOptions$Builder</className>
+    <method>com.google.cloud.spanner.SessionPoolOptions$Builder setUseMultiplexedSession(boolean)</method>
+  </difference>
 </differences>

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SessionPoolOptions.java

@@ -755,7 +755,7 @@ Builder setPoolMaintainerClock(Clock poolMaintainerClock) {
      * SessionPoolOptions#maxSessions} based on the traffic load. Failing to do so will result in
      * higher latencies.
      */
-    public Builder setUseMultiplexedSession(boolean useMultiplexedSession) {
+    Builder setUseMultiplexedSession(boolean useMultiplexedSession) {
       this.useMultiplexedSession = useMultiplexedSession;
       return this;
     }