Include number lookup logic for calibration

Based on this problem pointed out by @charlie.hoy, the lookup logic should be updated to account for the fact that there are now files with the syntax calibration_uncertainty_{ifo}_{time}_pydarm.txt in the calibration directories. Since the lookup logic looks backwards from ".txt" to search the numeric characters, this update will make it so any file with non-numeric characters directly before ".txt" do not get globbed (since these are the files we don't want anyway).