List BuildDriverValue as not shareable.

BuildDriverValue is just a wrapper value that signals that the building of a top level target was concluded. It's meant to be created anew each build, since BuildDriverFunction must be run every build.

PiperOrigin-RevId: 479029692
Change-Id: I701a9c371cc59d9aab7e3288a03fae7688874d80
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/BuildDriverKey.java b/src/main/java/com/google/devtools/build/lib/skyframe/BuildDriverKey.java
index 37255ba..6276d35 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/BuildDriverKey.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/BuildDriverKey.java
@@ -136,6 +136,14 @@
     return String.format("ActionLookupKey: %s; TestType: %s", actionLookupKey, testType);
   }
 
+  @Override
+  public boolean valueIsShareable() {
+    // BuildDriverValue is just a wrapper value that signals that the building of a top level target
+    // was concluded. It's meant to be created anew each build, since BuildDriverFunction must be
+    // run every build.
+    return false;
+  }
+
   enum TestType {
     NOT_TEST,
     PARALLEL,