Fix Merkle tree caching for runfiles trees.

After the refactoring in 404d8d9, runfile trees are registered with the wrong visitor.

Fixes #21628.

PiperOrigin-RevId: 614696699
Change-Id: Id13a47878c8c4a6390950397f8be0af7e61b6c75

src/main/java/com/google/devtools/build/lib/exec/SpawnInputExpander.java

@@ -438,7 +438,7 @@ public void visitNonLeaves(InputVisitor childVisitor)
                     inputMetadataProvider.getRunfilesMetadata(input).getRunfilesTree(),
                     artifactExpander,
                     pathMapper,
-                    visitor);
+                    childVisitor);
               }
             }