Use ruby slim image instead of alpine

We are seeing the following error when this Github action is executed:

ERROR: glibc-2.34-r0: trying to overwrite etc/nsswitch.conf owned by alpine-baselayout-data-3.2.0-r23.

There seems to be a problem when it attempts to install glibc, which is
needed as a native dependency for dartsass.

This commit resolves this by using a slim image instead of alpine,
which already includes the `glibc` package, so it doesn't need to be
explicitly installed.

We need to install the `build-essential` package so that native gem
dependencies are installed successfully. Otherwise we recieve the
following error when installing native dependencies for the racc gem,
which is a dependency of nokogiri:

current directory: /usr/local/bundle/gems/racc-1.7.3/ext/racc/cparse
make DESTDIR\= sitearchdir\=./.gem.20231114-7-jo9434 sitelibdir\=./.gem.20231114-7-jo9434 clean
current directory: /usr/local/bundle/gems/racc-1.7.3/ext/racc/cparse
make DESTDIR\= sitearchdir\=./.gem.20231114-7-jo9434 sitelibdir\=./.gem.20231114-7-jo9434
make failedNo such file or directory - make

The `rm -rf /var/lib/apt/lists/*` part will clear the package data and
help keep the overall image size small.

We are targeting ruby v3.1.4, as this matches the version we currently
use in the easol Rails app.

Dockerfile

@@ -1,4 +1,6 @@
-FROM ruby:3.2.1-alpine
+FROM ruby:3.1.4-slim
+
+RUN apt update && apt install -y build-essential && rm -rf /var/lib/apt/lists/*
 
 COPY entrypoint.sh /entrypoint.sh
 

entrypoint.sh

@@ -1,10 +1,5 @@
 #!/bin/sh
 
-# This is needed as native dependencies for dartsass
-wget -q -O /etc/apk/keys/sgerrand.rsa.pub https://alpine-pkgs.sgerrand.com/sgerrand.rsa.pub
-wget https://github.com/sgerrand/alpine-pkg-glibc/releases/download/2.34-r0/glibc-2.34-r0.apk
-apk add glibc-2.34-r0.apk
-
 gem install easol-canvas --version='~> 4.1'
 
 canvas lint