DEV: Fix methods removed in Ruby 3.2 (#15459)

* File.exists? is deprecated and removed in Ruby 3.2 in favor of
File.exist?
* Dir.exists? is deprecated and removed in Ruby 3.2 in favor of
Dir.exist?

spec/components/common_passwords/common_passwords_spec.rb

@@ -5,7 +5,7 @@ require "rails_helper"
 describe CommonPasswords do
 
   it "the passwords file should exist" do
-    expect(File.exists?(described_class::PASSWORD_FILE)).to eq(true)
+    expect(File.exist?(described_class::PASSWORD_FILE)).to eq(true)
   end
 
   describe "#common_password?" do

spec/components/oneboxer_spec.rb

@@ -5,7 +5,7 @@ require 'rails_helper'
 describe Oneboxer do
   def response(file)
     file = File.join("spec", "fixtures", "onebox", "#{file}.response")
-    File.exists?(file) ? File.read(file) : ""
+    File.exist?(file) ? File.read(file) : ""
   end
 
   it "returns blank string for an invalid onebox" do

spec/components/plugin/instance_spec.rb

@@ -230,11 +230,11 @@ describe Plugin::Instance do
       # calls ensure_assets! make sure they are there
       expect(plugin.assets.count).to eq(1)
       plugin.assets.each do |a, opts|
-        expect(File.exists?(a)).to eq(true)
+        expect(File.exist?(a)).to eq(true)
       end
 
       # ensure it cleans up all crap in autogenerated directory
-      expect(File.exists?(junk_file)).to eq(false)
+      expect(File.exist?(junk_file)).to eq(false)
     end
 
     it "registers auth providers correctly" do