Set default value of incompatible_load_argument_is_label to true.

RELNOTES:
  First argument of 'load' must be a label. Path syntax is removed.
  (label should start with '//' or ':').
PiperOrigin-RevId: 177802628
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java
index 685570b..534416a 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java
@@ -73,7 +73,7 @@
           .incompatibleDisallowToplevelIfStatement(true)
           .incompatibleDisallowUncalledSetConstructor(false)
           .incompatibleListPlusEqualsInplace(true)
-          .incompatibleLoadArgumentIsLabel(false)
+          .incompatibleLoadArgumentIsLabel(true)
           .incompatibleNewActionsApi(false)
           .incompatibleShowAllPrintMessages(true)
           .incompatibleStringIsNotIterable(false)