Do not require logger in common_logger spec

logger is moving from stdlib to bundled gems in Ruby 3.5, and will
be warning in Ruby 3.4.  This is the only code in Roda that requires
logger, and it's not necessary.

spec/plugin/common_logger_spec.rb

@@ -1,7 +1,5 @@
 require_relative "../spec_helper"
 
-require 'logger'
-
 describe "common_logger plugin" do
   def cl_app(&block)
     app(:common_logger, &block)
@@ -28,7 +26,10 @@ def cl_app(&block)
     @logger.rewind
     @logger.read.must_match(/\A1\.1\.1\.2 - - \[\d\d\/[A-Z][a-z]{2}\/\d\d\d\d:\d\d:\d\d:\d\d [-+]\d\d\d\d\] "GET \/a\/b\?foo=bar HTTP\/1.0" 200 2 0.\d\d\d\d\n\z/)
 
-    @app.plugin :common_logger, Logger.new(@logger)
+    logger = Struct.new(:logger) do
+      def <<(m) logger << m; end
+    end.new(@logger)
+    @app.plugin :common_logger, logger
     @logger.rewind
     @logger.truncate(0)
     body("HTTP_VERSION"=>'HTTP/1.0').must_equal '/'