Update CI scripts to test on different versions of Ruby and rnp

Codecov Report

Patch coverage: 50.00% and project coverage change: +0.04 :tada:

Comparison is base (d257020) 98.37% compared to head (5c765de) 98.42%.

:exclamation: Current head 5c765de differs from pull request most recent head d5e15a2. Consider uploading reports for the commit d5e15a2 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #85 +/- ## ========================================== + Coverage 98.37% 98.42% +0.04% ========================================== Files 42 41 -1 Lines 3333 3299 -34 ========================================== - Hits 3279 3247 -32 + Misses 54 52 -2 ``` | [Impacted Files](https://codecov.io/gh/rnpgp/ruby-rnp/pull/85?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rnpgp) | Coverage Δ | | |---|---|---| | [lib/rnp/misc.rb](https://codecov.io/gh/rnpgp/ruby-rnp/pull/85?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rnpgp#diff-bGliL3JucC9taXNjLnJi) | `98.85% <ø> (-1.15%)` | :arrow_down: | | [spec/generate/generate\_spec.rb](https://codecov.io/gh/rnpgp/ruby-rnp/pull/85?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rnpgp#diff-c3BlYy9nZW5lcmF0ZS9nZW5lcmF0ZV9zcGVjLnJi) | `99.40% <50.00%> (ø)` | | ... and [13 files with indirect coverage changes](https://codecov.io/gh/rnpgp/ruby-rnp/pull/85/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rnpgp) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rnpgp). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=rnpgp)

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rnpgp / ruby-rnp

Update CI scripts to test on different versions of Ruby and rnp #85

Codecov Report