These steps are useful if your CI run needs additional packages.
Usually they are declared as dependencies in your DESCRIPTION,
but it is also possible to install dependencies manually.
By default, binary versions of packages are installed if possible,
even if the CRAN version is ahead.
A step_install_deps() step installs all package dependencies declared in
DESCRIPTION, using remotes::install_deps().
This includes upgrading outdated packages.
A step_install_cran() step installs one package from CRAN via
install.packages(), but only if it's not already installed.
A step_install_github() step installs one or more packages from GitHub
via remotes::install_github(), the packages are only installed if their
GitHub version is different from the locally installed version.