Add .ruby-version file

Author: eggplants

.gitignore

@@ -2,7 +2,6 @@ build/*
 _site/*
 .bundle
 .idea
-.ruby-version
 .sass-cache
 tmp
 app/application.js

.ruby-version

@@ -0,0 +1 @@
+3.4.8

Dockerfile

@@ -2,6 +2,7 @@
 FROM ruby:3.4.8-slim-trixie AS builder
 # install build dependencies
 RUN apt update && apt install make gcc g++ libffi-dev nodejs git -y
+COPY ./.ruby-version /app/.ruby-version
 COPY ./Gemfile /app/Gemfile
 COPY ./Gemfile.lock /app/Gemfile.lock
 WORKDIR /app