Bugfix: RPC/blockchain: Correct description of getblockchaininfo's pruneheight result

It is possible that lower blocks are complete due to being stored in the same file as blocks not yet eligible for pruning.

Author: luke-jr

src/rpc/blockchain.cpp

@@ -1179,7 +1179,7 @@ RPCHelpMan getblockchaininfo()
                 {RPCResult::Type::STR_HEX, "chainwork", "total amount of work in active chain, in hexadecimal"},
                 {RPCResult::Type::NUM, "size_on_disk", "the estimated size of the block and undo files on disk"},
                 {RPCResult::Type::BOOL, "pruned", "if the blocks are subject to pruning"},
-                {RPCResult::Type::NUM, "pruneheight", /*optional=*/true, "lowest-height complete block stored (only present if pruning is enabled)"},
+                {RPCResult::Type::NUM, "pruneheight", /*optional=*/true, "height of the last block pruned, plus one (only present if pruning is enabled)"},
                 {RPCResult::Type::BOOL, "automatic_pruning", /*optional=*/true, "whether automatic pruning is enabled (only present if pruning is enabled)"},
                 {RPCResult::Type::NUM, "prune_target_size", /*optional=*/true, "the target size used by pruning (only present if automatic pruning is enabled)"},
                 {RPCResult::Type::OBJ_DYN, "softforks", /*optional=*/true, "(DEPRECATED, returned only if config option -deprecatedrpc=softforks is passed) status of softforks",