Make rules_ruby a dev-only dependency.

There is no canonical rules_ruby repo today, and we don't want our fork to become one.  In order to unblock inclusion of Protobuf in the bzlmod registry, we're making this a dev dependency and dropping support for Bazel/Ruby.

Fixes #14569

PiperOrigin-RevId: 584393841
diff --git a/conformance/BUILD.bazel b/conformance/BUILD.bazel
index 5558e87..5b9e1da 100644
--- a/conformance/BUILD.bazel
+++ b/conformance/BUILD.bazel
@@ -2,7 +2,8 @@
 
 load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library", "cc_proto_library", "objc_library")
 load("@rules_ruby//ruby:defs.bzl", "ruby_binary")
-load("//:protobuf.bzl", "internal_csharp_proto_library", "internal_objc_proto_library", "internal_php_proto_library", "internal_py_proto_library", "internal_ruby_proto_library")
+load("//ruby:defs.bzl", "internal_ruby_proto_library")
+load("//:protobuf.bzl", "internal_csharp_proto_library", "internal_objc_proto_library", "internal_php_proto_library", "internal_py_proto_library")
 load("//build_defs:internal_shell.bzl", "inline_sh_binary")
 load(
     "@rules_pkg//:mappings.bzl",
@@ -347,8 +348,7 @@
     visibility = ["//ruby:__subpackages__"],
     deps = [
         ":conformance_ruby_proto",
-        "//:test_messages_proto2_ruby_proto",
-        "//:test_messages_proto3_ruby_proto",
+        "//ruby:conformance_test_ruby_proto",
     ],
 )