Bump .ruby-version from 3.0.6 to 3.3.6

[amoeba]

This repo includes a .ruby-version file and the Gemfile refers to this. The site can be built with other Ruby versions but:

1. I think It's best to keep whatever version we specify in .ruby-version to something that's in support. Ruby 3.0.6 is not.
2. Our GHA workflows use ruby/setup-ruby which uses the Ruby version specified in .ruby-version which is another reason to specify an in support version of Ruby

I chose Ruby 3.3.6 because it's the latest release as of writing.

I've tested this PR locally by:

• Bundling under Ruby 3.3.6
• Generating the site (bundle exec generate)

And all looks good.

[lidavidm]

@kou any concerns?

[kou]

+1

No concern! If we have any problem, I can fix them.