workspace: bump rules_pkg

This updates rules_pkg to 0.5.1 and registers its dependencies so that
we can actually use it.

Change-Id: I4f9c225bfaed05da7a85c88f707df96b6ce1f1ce
Reviewed-on: https://review.monogon.dev/c/monogon/+/429
Reviewed-by: Sergiusz Bazanski <serge@monogon.tech>
diff --git a/WORKSPACE b/WORKSPACE
index fcf5197..2c26144 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -96,10 +96,17 @@
 # Build packages
 http_archive(
     name = "rules_pkg",
-    sha256 = "5bdc04987af79bd27bc5b00fe30f59a858f77ffa0bd2d8143d5b31ad8b1bd71c",
-    url = "https://github.com/bazelbuild/rules_pkg/releases/download/0.2.0/rules_pkg-0.2.0.tar.gz",
+    sha256 = "a89e203d3cf264e564fcb96b6e06dd70bc0557356eb48400ce4b5d97c2c3720d",
+    urls = [
+        "https://mirror.bazel.build/github.com/bazelbuild/rules_pkg/releases/download/0.5.1/rules_pkg-0.5.1.tar.gz",
+        "https://github.com/bazelbuild/rules_pkg/releases/download/0.5.1/rules_pkg-0.5.1.tar.gz",
+    ],
 )
 
+load("@rules_pkg//:deps.bzl", "rules_pkg_dependencies")
+
+rules_pkg_dependencies()
+
 # Rust rules
 http_archive(
     name = "rules_rust",