Currently many GitHub projects are changing the default branch from master to main.  Some projects have both branches.  The following produce different results:

Shell:

git clone url #checks out main

Pipeline:

git 'url' # checks out master 

It is certainly possible to specify a branch in both git and checkout step, but the default behavior is unintuitive.  As the default branch switch to main continues, I expect to encounter many (more) projects that have both branches (for better or for worse).

I noticed that docs were recently updated (JENKINS-64320), but I don't believe that every job referencing a repository (in this way) should change when the upstream default branch configuration changes.