Conda.jl error in GitHub actions

I have trouble with Conda.jl in GitHub actions. Since yesterday, I get the error

ERROR: LoadError: ArgumentError: Path to conda environment is not valid: /home/runner/.julia/conda/3

see test main · ranocha/BSeries.jl@8f68732 · GitHub. Note that I didn’t change anything important in that PR, see test main by ranocha · Pull Request #44 · ranocha/BSeries.jl · GitHub.

Everything was fine on main six days ago, see simplify CI cache (#41) · ranocha/BSeries.jl@c586858 · GitHub. I set the environment variable PYTHON = "", see BSeries.jl/CI.yml at main · ranocha/BSeries.jl · GitHub.

Any idea what might have changed since last week and how to fix the issue?

It looks like it might be a missing build step, see use test/Project.toml by ranocha · Pull Request #46 · ranocha/BSeries.jl · GitHub.