Add Ruby 3.0 support

Author: HarlemSquirrel

.github/workflows/test.yml

@@ -22,6 +22,7 @@ jobs:
           - "2.5"
           - "2.6"
           - "2.7"
+          - "3.0"
           - "jruby-9.2"
     steps:
     - uses: actions/checkout@v2

docker-compose.yml

@@ -66,6 +66,20 @@ services:
       - .:/code
     working_dir: /code
 
+  ci-3.0:
+    image: ruby:3.0
+    entrypoint: /code/ci-run.sh
+    environment:
+      INTEGRATION: openldap
+      INTEGRATION_HOST: ldap.example.org
+    depends_on:
+      - openldap
+    networks:
+      integration_test_network:
+    volumes:
+      - .:/code
+    working_dir: /code
+
   ci-jruby-9.2:
     image: jruby:9.2
     entrypoint: /code/ci-run.sh