Use pick method instead of pick_channels as it is now an MNE legacy function

[alexenge]

Running the pipeline with a recent version of MNE (e.g., 1.4) prints the following warning a couple of times:

NOTE: pick_channels() is a legacy function. New code should use inst.pick(...).

To resolve this, it should be enough to replace all something.pick_channels(...) calls with something.pick(...). Apparently, the standalone function (not the method) mne.pick_channels remains okay and does not need to be changed.

The new pick method is available since MNE 0.24, so it should be fairly safe to use since probably nobody using the pipeline will be on an older MNE version.