Update GitHub actions configuration

[ahukkanen]

• Update actions/checkout to v7
• Update codecov/codecov/action to v7
• Remove "Install dependencies" from both actions as this is already handled by the bundler-cache: true configuration

For the last item, see:
https://github.com/ruby/setup-ruby#caching-bundle-install-automatically

Note that any step doing bundle install (for the root Gemfile) or gem install bundler can be removed with bundler-cache: true.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (dead3ab) to head (87f6ab4).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #47   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           15        15           
  Lines          363       366    +3     
=========================================
+ Hits           363       366    +3     

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