Test Ruby 3.4; Upgrade actions workflows versions

[frederikspang]

Description

Describe your changes:

Upgrades tons of actions/checkout@v1 to v4, add 3.4 to build matrix.

Other questions: Ruby 2.4 is supported and tested, although it's EOL since 2020. Same goes for all versions through 3.0 actually, in yearly increments.

I'm all for keeping the test suite including some EOL versions, but 2.4 seems excessive.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.18%. Comparing base (ad535cc) to head (a278f36).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2506      +/-   ##
==========================================
- Coverage   98.20%   98.18%   -0.02%     
==========================================
  Files         128      128              
  Lines        4837     4839       +2     
==========================================
+ Hits         4750     4751       +1     
- Misses         87       88       +1     

Components	Coverage Δ
sentry-ruby	98.57% <100.00%> (ø)
sentry-rails	97.07% <100.00%> (ø)
sentry-sidekiq	97.02% <ø> (-0.41%)	⬇️
sentry-resque	92.85% <ø> (ø)
sentry-delayed_job	95.65% <ø> (ø)
sentry-opentelemetry	99.31% <ø> (ø)

Files with missing lines	Coverage Δ
sentry-rails/lib/sentry/rails/backtrace_cleaner.rb	100.00% <100.00%> (ø)
...b/sentry/rails/tracing/active_record_subscriber.rb	96.36% <ø> (ø)
sentry-ruby/lib/sentry/backtrace.rb	96.72% <100.00%> (ø)

... and 1 file with indirect coverage changes

[solnic]

Thank you! We need to support ancient Rubies as long as Sentry customers use them 😅

[frederikspang]

To be fair, as long as it's not an excessive work, it's fine!

We have a 2.7.x app running as well😄