Fix specs, update CI matrix

Author: Envek

.github/workflows/test.yml

@@ -23,6 +23,7 @@ jobs:
           - '3.1'
           - '3.2'
           - '3.3'
+          - '3.4'
     steps:
       - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1

lib/yabeda/prometheus/exporter.rb

@@ -2,6 +2,7 @@
 
 require "prometheus/middleware/exporter"
 require "rack"
+require "logger"
 
 module Yabeda
   module Prometheus