Fix external-file ImageSeries test and require pynwb>=4.0#708

rly merged 4 commits into

devNeurodataWithoutBorders/nwbinspector:devfrom

fix/image-series-num-samples-pynwb-4NeurodataWithoutBorders/nwbinspector:fix/image-series-num-samples-pynwb-4Copy head branch name to clipboard