Update Jekyll to latest 3.x to support Ruby 3 Debian ships Ruby 3.1.2 and Jekyll 3.9.5 manages to build and serve the pages. I had to explicitly add `kramdown-parser-gfm`. Ruby 3 moved `rexml` and `webrick` out of the standard library. Also update the Dockerfile base to Ruby 3.3. Change-Id: I8702537dde1acd5ce272e1babac70ec480781353
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