`npm test` fails to run on Windows (`test/run.sh` is not executed)

[GerHobbelt]

This is due to the particulars on Windows where the usual install of git-on-windows has a bash shell, but this is not the default command shell (for obvious reasons as then quite a lot of other unrelated things would fail), so any npm script task which executes a UNIX shell script should do this by invoking bash -c <script_path> instead of just invoking <script_path>.