Fix first occuring event search for backward integration

[dcourteville]

Checklist

• Appropriate tests were added: I will open a PR on OrdinaryDiffEq.jl with the tests
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Fix for #1231

[ChrisRackauckas]

add the mwe in the downstream test sets

[dcourteville]

Done : SciML/OrdinaryDiffEq.jl#2933

[dcourteville]

Sorry, I added the tests in the downstream folder here.