User avatar responses have cache-control "public"

ref: https://app.fizzy.do/5986089/cards/3125

app/controllers/users/avatars_controller.rb

@@ -32,7 +32,7 @@ class Users::AvatarsController < ApplicationController
       if @user == Current.user
         {}
       else
-        { max_age: 30.minutes, stale_while_revalidate: 1.week }
+        { max_age: 30.minutes, stale_while_revalidate: 1.week, public: true }
       end
     end
 

test/controllers/users/avatars_controller_test.rb

@@ -15,6 +15,7 @@ class Users::AvatarsControllerTest < ActionDispatch::IntegrationTest
   test "show other initials with caching" do
     get user_avatar_path(users(:kevin))
     assert_match "image/svg+xml", @response.content_type
+    assert @response.cache_control[:public]
     assert_equal 30.minutes.to_s, @response.cache_control[:max_age]
   end