Flip `--@rules_java//toolchains:incompatible_language_version_bootclasspath` to `True`

Fixes https://github.com/bazelbuild/rules_java/issues/387

PiperOrigin-RevId: 1007841736
Change-Id: I5fd223963b3bc7ce258d330092683ad58c1bdda9

toolchains/BUILD

diff --git a/toolchains/BUILD b/toolchains/BUILD
index e605607..9eca53d 100644
--- a/toolchains/BUILD
+++ b/toolchains/BUILD
@@ -44,7 +44,7 @@
 # `--java_runtime_version`.
 bool_flag(
     name = "incompatible_language_version_bootclasspath",
-    build_setting_default = False,
+    build_setting_default = True,
     visibility = ["//visibility:private"],
 )