Describe the workflow you want to enable

7b71511 moved duplicated code above the conditional statements, but this means that an expensive step for computing GPR variances is executed even if bothreturn_std andreturn_cov areFalse. Profiling shows this takes ~96% of the computation time. I would like to see they_mean value returned before this step to save time.

Describe your proposed solution

AboveV = solve_triangularhttps://github.com/scikit-learn/scikit-learn/blob/main/sklearn/gaussian_process/_gpr.py#L454, add

if not return_std and not return_cov:    return y_mean

Describe alternatives you've considered, if relevant

No response

Additional context

No response