Issue:
All Bitrise stacks have Ruby pre-installed, with several different available versions. However, your app's Gemfile might specify a Ruby version that isn't installed on any Bitrise stack and thus certain Steps, such as the Run Cocoapods install, might fail.
Possible solutions:
You can either change your Gemfile and specify an installed Ruby version, or install the correct Ruby version on the virtual machine itself.
To install the version:
1. Add a Script Step to your Workflow.
2. Go to the Script content input.
3. In the input field, add the following:
# Install the minor version you want - in this example we're installing 3.1.2:
asdf install ruby 3.1.2
# Set it as your default version of Ruby:
asdf global ruby 3.1.2
asdf local ruby 3.1.2