CI: macos-13 for Ruby 2.5

[olleolleolle]

This uses now-compatible "os" choices for Ruby 2.4, 2.5.

This failed in the build of #31.

I enabled fail-fast: false to be able to iterate on the CI workflow.

Details

Found this:

Bundler found conflicting requirements for the Ruby version:
  In Gemfile:
    tempfile was resolved to 0.2.1, which depends on
      Ruby (>= 2.5.0)

  Current Ruby version:
    Ruby (= 2.4.10)

EDIT: Noted that I had wrongly added 2.4 I am removing the 2.4 from the workflow.

Also: There are errors about a Tempfile lacking a filename in the failed tests. (These are for Ruby versions 3.1 and below.)

[olleolleolle]

Did the "anonymous: true" change fail for these (< Ruby 3.2) versions?
57e9af4

[olleolleolle]

I suggest we merge this PR, to have better visibility on master about what CI results we have.

[hsbt]

@olleolleolle Thanks for rising this. I added workaround for that at #35

[olleolleolle]

@hsbt Perfect fix!