Add global PackageSpecificationInfo (#58)

private/globals.bzl

diff --git a/private/globals.bzl b/private/globals.bzl
index a29210a..97b6ec6 100644
--- a/private/globals.bzl
+++ b/private/globals.bzl
@@ -3,6 +3,9 @@
 # Access any of these globals via bazel_features.globals.<name>
 # If the current version of Bazel doesn't have this global, it will be None.
 GLOBALS = {
+    # https://github.com/bazelbuild/bazel/commit/d1d35b280af1459458f996502e255d3774f391c2
+    "PackageSpecificationInfo": "6.4.0",
+    
     # https://github.com/bazelbuild/bazel/pull/15232
     "RunEnvironmentInfo": "5.3.0",