ci: run tests on more versions of nvim

Summary:

Right now we are only running the tests on the nightly build of nvim. I would
like to try and maintain support for a few releases. One of the goals of this
project is to be stable. This means trying our best to maintain BC, for this I
have setup running the tests on older versions of nvim.

Right now we have:

• *nightly* Make sure we support the new releases, we can hopefully fix issues before this gets releases.
• *stable* This is the main version we support
• *v0.9.5* Maintain the old stable, some OSs like Ubuntu lack behind, would be nice to maintain that.

Test Plan:

CI, I have done a quick run before finalizing the change