Cannot install new ruby version with rbenv

[kelianClerc]

Cannot access install command for rbenv from a github action. This command is well installed via

# Install ruby-build (rbenv plugin)
RUN mkdir -p "$RBENV_HOME"/plugins
RUN git clone https://github.com/rbenv/ruby-build.git "$RBENV_HOME"/plugins/ruby-build

But when trying to run it from a github action, I've got the following error :
https://github.com/faberNovel/faberdemo-android/runs/923377141?check_suite_focus=true

According to stackoverflow, to load plugins, a configuration is missing
https://stackoverflow.com/a/24249090/7301610

[sjcqs]

After some digging with @kelianClerc:

• Github Action is changing HOME env var to /github/workspace
  Thus, rbenv plugins are not available anymore.

To fix it RBENV_ROOT need to be set.