Upgrade Mastodon to 4.7.4

Bump the runtime Ruby to 4.0.9 (and the ruby-build definitions to
v20261023, the first release that defines it), matching upstream's
updated default Ruby for the 4.7.4 security release.

site-cookbooks/kosmos-mastodon/attributes/default.rb

@@ -19,8 +19,8 @@ node.default["kosmos-mastodon"]["build"] = true
 
 # Runtime versions
 node.default["kosmos-mastodon"]["nodejs_version"]      = "24.22.1"
-node.default["kosmos-mastodon"]["ruby_version"]        = "4.0.7"
-node.default["kosmos-mastodon"]["ruby_build_version"]  = "v20260924"
+node.default["kosmos-mastodon"]["ruby_version"]        = "4.0.9"
+node.default["kosmos-mastodon"]["ruby_build_version"]  = "v20261023"
 
 # SSH deploy key access to the (private) repository. The private key is stored
 # in the credentials/mastodon data bag as `repo_deploy_key`; this is the pinned