Merge bitcoin/bitcoin#23929: doc: fix undo data filename (s/undo???.dat/rev???.dat/)

2e42050 doc: fix undo data filename (s/undo???.dat/rev???.dat/) (Sebastian Falbesoner)

Pull request description:

  This typo was discovered in the course of a review club to #20827, see https://bitcoincore.reviews/20827#l-31.

ACKs for top commit:
  shaavan:
    ACK 2e42050

Tree-SHA512: 0c7a00dce24c03bee6d37265d5b4bc97e976c3f3910af1113f967f6298940f892d6fb517f7b154f32ccedb365060314d4d78d5eb2a9c68b25f0859a628209cd3

Author: fanquake

src/validation.h

@@ -402,7 +402,7 @@ class BlockManager
     void FindFilesToPruneManual(std::set<int>& setFilesToPrune, int nManualPruneHeight, int chain_tip_height);
 
     /**
-     * Prune block and undo files (blk???.dat and undo???.dat) so that the disk space used is less than a user-defined target.
+     * Prune block and undo files (blk???.dat and rev???.dat) so that the disk space used is less than a user-defined target.
      * The user sets the target (in MB) on the command line or in config file.  This will be run on startup and whenever new
      * space is allocated in a block or undo file, staying below the target. Changing back to unpruned requires a reindex
      * (which in this case means the blockchain must be re-downloaded.)