GitHub Pages build is broken

[Haprog]

See failed build here https://github.com/solita/solita.github.com/actions/runs/7897753738

Probably caused by GitHub updating some dependencies of the built in Pages builder.
We can be more in control here by starting to use a custom GitHub Action to do the Jekyll build for generating and deploying GitHub Pages instead of using the current zero-config process.

Seems like these issues are related to the problem:

• [Bug]: Error: undefined method `excerpt_separator' for #<Jekyll::Page> jekyll/jekyll#9544
• undefined method `excerpt_separator'  actions/jekyll-build-pages#115

From what I understand it seems the issue manifests when using actions/jekyll-build-pages versions 1.0.10 or 1.0.11 (currently latest and default for GH pages classic build) but you could use older 1.0.9 via custom GH action. The open issue above is in the main jekyll repository so that Jekyll 3.9.4 and 3.9.5 apparently have some issue but that alone doesn't seem to cause the problem in this repo as even those versions seem to work fine in some situations (e.g. when testing locally). Maybe it's a combinations of dependencies that triggers the problem when using those latest versions of jekyll-build-pages.