Add MSH SpikeGadgets fixture to CI

[h-mayorquin]

This PR adds new testing dataset to the CI.

This tests device="intan" + chanPerChip="0" Intan-fallback code path (added to gin in PR #174).

I also did some small improvements:

• Warn (logger.warning) when chanPerChip > num_ephy_channels, which surfaces bogus header values like the chanPerChip="1645402192" case reported in #1830.
• Sort the fallback hwChan list ascending, since the Trodes writer writes the binary in hwChan-indexed order regardless of deviceType. This will be a safeguard in case someone modifies the xml by themselves as we are using this assumption for correct mapping of channels to binary layout.