ITKUltrasound notebook checks possibly running against previous versions

[tbirdso]

In #176 notebook CI checks seem to fail with the bug that is present in the released 0.5.1 package which the PR aims to fix and tag 0.5.2. My guess is that the notebook CI is pip installing the most recent ITKUltrasound package and running notebooks with it. If this is verified to the case, we should revisit how/when we are running notebook CI.

If notebook CI does not reflect individual changes but rather tags, we should refactor so that these CI tests do not run in PRs and only run on the master branch (or maybe even only when a tagged version is released, if possible).

It seems reasonable to still run notebook CI occasionally to ensure that input data or notebook processes are not invalidated, as long as it is clearly recognized that changes since the previous tag are not reflected.