github/workflows: add autotick workflow

[proppy]

• fetch latest version from https://anaconda.org/litex-hub/ channel
• replace package version in notebooks cells
• create PR (that will trigger CI #55)

Fixes #60

[proppy]

@mithro fyi @umarcor does that seems reasonable? @msaligane that might be useful for https://github.com/sscs-ose/sscs-ose-code-a-chip.github.io

[umarcor]

@proppy I'm not fond of having CI create PRs automatically, because it needs write permissions and that's cumbersome to handle with regard to contributors/forks. Hence, I would recommend to add the script and run the workflow periodically to check whether something is to be updated; but let a human actually commit the changes.