radare2: add "extras" resource for HEAD too

This fixes a minor regression introduced by 4df5bd4

Closes Homebrew/homebrew#49102.
Closes Homebrew/homebrew#49134.

Signed-off-by: Dominyk Tiller <dominyktiller@gmail.com>

Formula/radare2.rb

@@ -29,6 +29,10 @@ class Radare2 < Formula
     resource "bindings" do
       url "https://github.com/radare/radare2-bindings.git"
     end
+
+    resource "extras" do
+      url "https://github.com/radare/radare2-extras.git"
+    end
   end
 
   depends_on "pkg-config" => :build