fix(test): Move local test to more current fish ...

... by means of using a more current OS, and
fix a test helper that used a feature now removed from fish.

test/Dockerfile

@@ -1,15 +1,17 @@
-FROM ruby:2.7-slim-buster
+FROM ubuntu
 
 # Install dependencies
 RUN apt-get update \
  && apt-get -y install \
-        fish \
+        build-essential \
         curl \
+        fish \
+        ruby \
+        ruby-dev \
         unzip \
         zip \
-        ruby-dev \
-        build-essential \
- && apt-get clean
+ && apt-get clean \
+ && gem install bundler
 
 WORKDIR app
 COPY test/Gemfile ./

test/features/support/helpers.rb

@@ -64,7 +64,7 @@ def run_fish_command(cmd)
     end.to_h
 
     out, status = Open3.capture2e(<<~FISH
-      fish -c '#{cmd} > #{files[:stdout]} ^ #{files[:stderr]}; \
+      fish -c '#{cmd} > #{files[:stdout]} 2> #{files[:stderr]}; \
                echo $status > #{files[:status]}; \
                env > #{files[:env]}; \
               '