Fix CI and simplify matrix

[st0012]

1. Since we only test against ubuntu-latest, I removed os from the matrix to simplify our workflow configs.
2. Because sentry-delayed_job still tests against Rails 7.0, which doesn't work with Ruby head atm due to mutex_m gem being migrated to bundled gem:

Failure/Error: require "active_record"

LoadError:
  cannot load such file -- mutex_m
# ./spec/spec_helper.rb:4:in `<top (required)>'
# ./spec/sentry/delayed_job/configuration_spec.rb:1:in `<top (required)>'

And I fixed it by excluding Ruby head from the matrix.

Ideally the fix should be to use Rails 7.1 for testing instead, but it's trickier than I thought. So I decided to fix it first and work on #2229 later.

skip-changelog

[codecov[bot]]

Codecov Report

Merging #2230 (559ed76) into master (d408bdd) will not change coverage. The diff coverage is n/a.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2230 +/- ## ======================================= Coverage 97.44% 97.44% ======================================= Files 102 102 Lines 3800 3800 ======================================= Hits 3703 3703 Misses 97 97 ``` | [Components](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2230/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | Coverage Δ | | |---|---|---| | [sentry-ruby](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2230/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `98.13% <ø> (ø)` | | | [sentry-rails](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2230/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `95.01% <ø> (ø)` | | | [sentry-sidekiq](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2230/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `94.70% <ø> (ø)` | | | [sentry-resque](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2230/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `93.65% <ø> (ø)` | | | [sentry-delayed_job](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2230/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `94.44% <ø> (ø)` | | | [sentry-opentelemetry](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2230/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `100.00% <ø> (ø)` | |