.github/workflows: do not add work in progress label by default

[sam-heilbron]

Description

Reverts the work in kgateway-dev#9849

Context

A number of slack threads opened by engineers about how this is confusing and leads to toil.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

[andy-fong]

I actually like the label being added automatically but I am ok either. Are we going to do the same for solo-projects? I know in solo-projects, the work in progress labels also prevent the regession tests from running.

[sam-heilbron]

/skip-ci non-functional change