Mark ruby_toolchains as a dev dependency

MODULE.bazel

diff --git a/MODULE.bazel b/MODULE.bazel
index acca7e2..6d30d8e 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -80,7 +80,7 @@
     gemfile_lock = "//ruby:Gemfile.lock",
 )
 use_repo(ruby, "protobuf_bundle", "ruby_toolchains")
-register_toolchains("@ruby_toolchains//:all")
+register_toolchains("@ruby_toolchains//:all", dev_dependency=True)
 
 # Proto toolchains
 register_toolchains("//bazel/private/toolchains:all")