Make ignore_interrupts thread-safe.

Library/Homebrew/extend/kernel.rb

@@ -349,7 +349,10 @@ module Kernel
     end
   end
 
+  IGNORE_INTERRUPTS_MUTEX = Thread::Mutex.new.freeze
+
   def ignore_interrupts(_opt = nil)
+    IGNORE_INTERRUPTS_MUTEX.synchronize do
       # rubocop:disable Style/GlobalVars
       $ignore_interrupts_nesting_level = 0 unless defined?($ignore_interrupts_nesting_level)
       $ignore_interrupts_nesting_level += 1
@@ -374,6 +377,7 @@ module Kernel
       end
       # rubocop:enable Style/GlobalVars
     end
+  end
 
   def redirect_stdout(file)
     out = $stdout.dup