MNT: turn off conda tests in pip_only branch

[tangkong]

An experimental branch, we can choose not to go this route if we like. I mostly want to stop filtering red ❌ on the BEAMS repo

Note: I'm requesting this branch be merged into the pcdshub:pip_only branch, not master

[ZLLentz]

I personally think its worth having a separate file for this as a standard option, along with a conda-only variant.
Starting as a branch is reasonable first step.