Refer to the proper filegroup, not to a directory

Without this change, //src/test/shell/bazel:bazel_toolchain_test is failing
when remote caching is enabled.

Workaround for #2845.

PiperOrigin-RevId: 153574893
diff --git a/src/test/shell/bazel/testdata/BUILD b/src/test/shell/bazel/testdata/BUILD
index da7f790..bd2a6fc 100644
--- a/src/test/shell/bazel/testdata/BUILD
+++ b/src/test/shell/bazel/testdata/BUILD
@@ -21,7 +21,7 @@
     name = "bazel_toolchain_test_project_pkg",
     testonly = 1,
     srcs = [
-        "bazel_toolchain_test_data",
+        "//src/test/shell/bazel/testdata/bazel_toolchain_test_data:srcs",
     ],
     visibility = ["//src/test/shell/bazel:__pkg__"],
 )