tap-info cmd: skip untapped core taps

When homebrew/core or homebrew/cask are untapped `brew tap-info` fails because
Tap.each includes them and tap.private? fails without a git repo interrogate.

This restores the behavior of `brew tap-info` before #16710

Library/Homebrew/cmd/tap-info.rb

@@ -48,7 +48,7 @@ module Homebrew
       formula_count = 0
       command_count = 0
       private_count = 0
-      Tap.each do |tap|
+      Tap.installed.each do |tap|
         tap_count += 1
         formula_count += tap.formula_files.size
         command_count += tap.command_files.size

Library/Homebrew/test/cmd/tap-info_spec.rb

@@ -13,4 +13,11 @@ RSpec.describe "brew tap-info" do
       .and not_to_output.to_stderr
       .and be_a_success
   end
+
+  it "display brief statistics for all installed taps", :integration_test, :needs_network do
+    expect { brew "tap-info", "HOMEBREW_NO_INSTALL_FROM_API" => nil }
+      .to output(/\d+ taps?, \d+ private/).to_stdout
+      .and not_to_output.to_stderr
+      .and be_a_success
+  end
 end