Fix CI failures

.github/workflows/test.yml

@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         # Due to https://github.com/actions/runner/issues/849, we have to use quotes for '3.0'
-        ruby: [2.6, 2.7, '3.0', 3.1, 'jruby-9.3']
+        ruby: [2.6, 2.7, '3.0', 'jruby-9.3']
     steps:
     - uses: actions/checkout@v2
     - uses: ruby/setup-ruby@v1

sinatra-contrib/lib/sinatra/config_file.rb

@@ -124,7 +124,11 @@ module Sinatra
             raise UnsupportedConfigType unless ['.yml', '.yaml', '.erb'].include?(File.extname(file))
             logger.info "loading config file '#{file}'" if logging? && respond_to?(:logger)
             document = ERB.new(IO.read(file)).result
-            yaml = YAML.load(document)
+            yaml = begin
+              YAML.load(document, aliases: true)
+            rescue ArgumentError
+              YAML.load(document)
+            end
             config = config_for_env(yaml)
             config.each_pair { |key, value| set(key, value) }
           end