Fix build with Bazel@HEAD

Broken by https://github.com/bazelbuild/bazel/pull/27674

(ignore-relnotes)

PiperOrigin-RevId: 874542646
Change-Id: I4f1e8c9baae8330d703d6f7eb145e5a3ee2923fc

java/BUILD

diff --git a/java/BUILD b/java/BUILD
index b613191..bcb113a 100644
--- a/java/BUILD
+++ b/java/BUILD
@@ -61,6 +61,11 @@
     visibility = ["//visibility:public"],
 )
 
+exports_files(
+    ["java_single_jar.bzl"],
+    visibility = ["//test:__pkg__"],
+)
+
 bzl_library(
     name = "java_single_jar",
     srcs = ["java_single_jar.bzl"],