Use buildOrThrow instead of build for ImmutableMap. (#3394)

This method have been added in guava 31, so we are also updating the dependency.

Author: rlazo

encoders/firebase-encoders-proto/firebase-encoders-proto.gradle

@@ -42,7 +42,7 @@ dependencies {
 
     testAnnotationProcessor project(':encoders:firebase-encoders-processor')
 
-    testImplementation 'com.google.guava:guava:30.0-jre'
+    testImplementation 'com.google.guava:guava:31.0-jre'
     testImplementation 'junit:junit:4.13.1'
     testImplementation 'com.google.protobuf:protobuf-java-util:3.11.0'
     testImplementation 'com.google.truth.extensions:truth-proto-extension:1.0'

encoders/firebase-encoders-proto/src/test/java/com/google/firebase/encoders/proto/WithCollectionsTests.java

@@ -51,7 +51,7 @@ public void test2() throws InvalidProtocolBufferException {
                     .put("noValue", new Fixed())
                     .put("value", new Fixed(1, 2, 3, 4))
                     .put("", new Fixed())
-                    .build(),
+                    .buildOrThrow(),
                 ImmutableList.of(
                     new OtherTypes("hello", new byte[0], false, true),
                     new OtherTypes("", new byte[] {42}, true, false),