DOCS-15408 update release candidate verbiage (#1250)

Author: ianf-mongodb

source/release-notes.txt

@@ -27,12 +27,12 @@ use on-premises.
      - Version
      - Release Notes
 
-   * - Upcoming Rapid Release
+   * - Current Rapid Release
      - 5.3-series
-     - `Release Notes for MongoDB 5.3 (Release Candidate)
+     - `Release Notes for MongoDB 5.3
        <https://docs.mongodb.com/v5.3/release-notes/5.3/>`__
 
-   * - Current Rapid Release
+   * - Previous Rapid Release
      - 5.2-series
      - `Release Notes for MongoDB 5.2
        <https://docs.mongodb.com/v5.2/release-notes/5.2/>`__