github_packages: Add platform.variant

Library/Homebrew/github_packages.rb

@@ -246,8 +246,21 @@ class GitHubPackages
         (tab["built_on"]["glibc_version"] if tab["built_on"].present?) || "2.23"
       end
 
+      variant = if architecture == "arm64"
+        "v8"
+      elsif tab["oldest_cpu_family"]
+        tab["oldest_cpu_family"]
+      elsif architecture == "amd64"
+        if os == "darwin"
+          Hardware.oldest_cpu(OS::Mac::Version.new(os_version[/macOS ([0-9]+\.[0-9]+)/, 1])).to_s
+        else
+          "core2"
+        end
+      end
+
       platform_hash = {
         architecture: architecture,
+        variant: variant,
         os: os,
         "os.version" => os_version,
       }