Drop support for Ruby 2.5

It's no longer supported by minitest, making
it hard to support.

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
-          ruby-version: "2.5"
+          ruby-version: "3.3"
           bundler-cache: true
       - name: Lint
         run: bundle exec rubocop
@@ -28,7 +28,7 @@ jobs:
       matrix:
         os: ["ubuntu-latest"]
         redis: ["6.2"]
-        ruby: ["ruby-head", "3.2", "3.1", "3.0", "2.7", "2.6", "2.5", "jruby-9.3.6.0", "truffleruby"]
+        ruby: ["ruby-head", "3.3", "3.2", "3.1", "3.0", "2.7", "2.6", "jruby-9.3.6.0", "truffleruby"]
     runs-on: ${{ matrix.os }}
     steps:
       - name: Check out code

redis-client.gemspec

@@ -11,7 +11,7 @@ Gem::Specification.new do |spec|
   spec.summary = "Simple low-level client for Redis 6+"
   spec.homepage = "https://github.com/redis-rb/redis-client"
   spec.license = "MIT"
-  spec.required_ruby_version = ">= 2.5.0"
+  spec.required_ruby_version = ">= 2.6.0"
 
   spec.metadata["allowed_push_host"] = "https://rubygems.org"