CI: Try Ruby 4.0.1 with Bundler 4.0.4

Author: dentarg

.github/workflows/test.yml

@@ -96,7 +96,7 @@ jobs:
           - "--enable-frozen-string-literal --debug-frozen-string-literal"
         include:
           # Avoid Bundler 4 for now: https://github.com/sinatra/sinatra/issues/2135
-          - { ruby: "4.0", bundler: 2.7.2, rack: stable, puma: stable, tilt: stable, rack_session: stable, zeitwerk: stable }
+          - { ruby: "4.0", bundler: 4.0.4, rack: stable, puma: stable, tilt: stable, rack_session: stable, zeitwerk: stable }
           # Rack
           - { ruby: 3.4, bundler: default, rack: "~>3.0.0", puma: stable, tilt: stable, rack_session: stable, zeitwerk: stable }
           - { ruby: 3.4, bundler: default, rack: "~>3.1.0", puma: stable, tilt: stable, rack_session: stable, zeitwerk: stable }