Add a couple missing @CIRV annotations.

RELNOTES=n/a
PiperOrigin-RevId: 466056991

Author: cgdecker

guava/src/com/google/common/collect/HashBiMap.java

@@ -333,6 +333,7 @@ public V forcePut(@ParametricNullness K key, @ParametricNullness V value) {
     return put(key, value, true);
   }
 
+  @CanIgnoreReturnValue
   @CheckForNull
   private K putInverse(@ParametricNullness V value, @ParametricNullness K key, boolean force) {
     int valueHash = smearedHash(value);

guava/src/com/google/common/collect/ImmutableSet.java

@@ -555,6 +555,7 @@ public Builder<E> addAll(Iterator<? extends E> elements) {
       return this;
     }
 
+    @CanIgnoreReturnValue
     Builder<E> combine(Builder<E> other) {
       requireNonNull(impl);
       requireNonNull(other.impl);