Enable --incompatible_disallow_dict_plus by default

Fixes #6461

RELNOTES: --incompatible_disallow_dict_plus is enabled by default
PiperOrigin-RevId: 234829823
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java b/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java
index f075118..fd40dd5 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java
@@ -218,7 +218,7 @@
           .incompatibleDisableDeprecatedAttrParams(false)
           .incompatibleDisableObjcProviderResources(false)
           .incompatibleDisallowDataTransition(true)
-          .incompatibleDisallowDictPlus(false)
+          .incompatibleDisallowDictPlus(true)
           .incompatibleDisallowFileType(true)
           .incompatibleDisallowLegacyJavaProvider(false)
           .incompatibleDisallowLegacyJavaInfo(false)