fix: fix the wrong return type for Pipeline.as(String alias) (#2330)

* Fix the wrong return type for Pipeline.as(String alias)

* chore: generate libraries at Fri Feb 27 19:17:30 UTC 2026

---------

Co-authored-by: cloud-java-bot <cloud-java-bot@google.com>

Author: cherylEnkidu

google-cloud-firestore/src/main/java/com/google/cloud/firestore/pipeline/expressions/Expression.java

@@ -4332,11 +4332,11 @@ public final Ordering descending() {
    * names to calculated values.
    *
    * @param alias The alias to assign to this expression.
-   * @return A new {@link Selectable} (typically an {@link AliasedExpression}) that wraps this
-   *     expression and associates it with the provided alias.
+   * @return A new {@link AliasedExpression} that wraps this expression and associates it with the
+   *     provided alias.
    */
   @BetaApi
-  public Selectable as(String alias) {
+  public AliasedExpression as(String alias) {
     return new AliasedExpression(this, alias);
   }