Do not run CI on non-master branches

[axmmisaka]

For non-master branches, they are probably all created for some PR and a duplication CI problem arises when a PR is created. It makes more sense to run CI only on master and PRs.

[lhstrh]

Note: the CI configuration changed on master of the lingua-franca repo. I noticed that you changed lingua-franca-ref.txt in #160, but that will require reworking ci.yml a little bit. I'm OK with only running CI on master and PRs through.

[axmmisaka]

I see; that definitely needs to be addressed and I'll look into it after #160 is ready to be reviewed......

[axmmisaka]

Note: the CI configuration changed on master of the lingua-franca repo. I noticed that you changed lingua-franca-ref.txt in #160, but that will require reworking ci.yml a little bit. I'm OK with only running CI on master and PRs through.

I think it works now? Thanks for the fix!