CircleCi Build is failing due to the wrong Ruby version - ruby

Question

We originally were using Ruby 2.2.3 for our application, however, now I'm updating the gems due to vulnerabilities and as a result, I have to update the ruby version that the application is running on. Locally, this was fairly straight forward (using rbenv), however, when I push it to GitHub, it fails the CircleCi build because it's pulling the ruby version from an old docker image that's using the old ruby version.
So far, I've pulled the old docker image down using docker pull, ran the image using docker run -it, opened it in VSCode using the Remote Extension, and downloaded rbenv, updated the ruby version, committed the changes with docker commit, pushed it to GitHub with docker push, and tested it but it's still failing the CircleCi build with an error saying that the updated gems need to use the updated version of ruby.
config.yml:
version: 2.1
jobs:
build:
docker:
- image: 073991710092.dkr.ecr.us-east-1.amazonaws.com/signage-dev:latest-v2
environment:
RAILS_LOG_TO_STDOUT: 'true'
RAILS_ENV: test
APP_ENV: development
DB_USERNAME: *******
DB_PASSWORD: *******
DB_HOST: mysql
CACHE_HOST: redis
TZ: "America/New_York"
- image: mysql:5.6.37
name: mysql
environment:
MYSQL_ROOT_PASSWORD: *******
MYSQL_USER: *******
MYSQL_PASSWORD: *******
MYSQL_DATABASE: *******
- image: redis:2.8.6
name: redis
command: redis-server
steps:
- checkout
- run:
name: setup
command: |
mkdir app/log
touch app/log/oink.log
chmod a+rw app/log/oink.log
touch app/rspec.xml
mkdir -p app/tmp/cache/assets/test/sprockets/v3.0
- run:
name: setup database
command: (cd ./app && gem install bundler && bundle install && bundle exec rake --trace db:setup)
- run:
name: run tests
command: |
cd ./app
mkdir /tmp/test-results
TEST_FILES="$(circleci tests glob "spec/**/*_spec.rb" | circleci tests split --split-by=timings)"
bundle exec rspec --format progress \
--format RspecJunitFormatter \
--out /tmp/test-results/rspec.xml \
--format progress \
$TEST_FILES
- store_test_results:
path: /tmp/test-results
- store_artifacts:
path: /tmp/test-results
destination: test-results
Here's what happens when I open the image in a container and check the ruby version:
docker run -it 073991710092.dkr.ecr.us-east-1.amazonaws.com/signage-dev:latest-v2 bash
root#836591d2e6bf:/# ls
Gemfile bin dev home lib media opt root sbin sys usr
Gemfile.lock boot etc index.html lib64 mnt proc run srv tmp var
root#836591d2e6bf:/# ruby -v
ruby 2.6.0p0 (2018-12-25 revision 66547) [x86_64-linux]
Error message in CircleCi (Setup Database):
#!/bin/bash -eo pipefail
(cd ./app && gem install bundler && bundle install && bundle exec rake --trace db:setup)
ERROR: Error installing bundler:
bundler requires Ruby version >= 2.3.0.
Exited with code exit status 1
CircleCI received exit code 1