CI: Create workflow to rebase this fork to the latest upstream tag

[EwoutH]

This workflow runs daily and opens a PR is there is a new tag available upstream, to sync it to that tag.

[EwoutH]

GitHub Actions needs to be enabled on https://github.com/scipy/HiGHS/actions for it to work, could a maintainer enable it?

[rgommers]

Thanks @EwoutH. Two issues I think I see with the mechanics of this:

• this is going to open a new PR for the same tag each day until the first PR is merged, isn't it?
• this action should not run on forks (that'd make the same mess that Dependabot makes)

@mckib2 what do you think? The notifications may be useful, assuming the issues above are taken care of.

[EwoutH]

Thanks for reviewing!

this is going to open a new PR for the same tag each day until the first PR is merged, isn't it?

Good remark! Fortunatly the peter-evans/create-pull-request step considers this, and only opens up a PR if there isn't one open already.

this action should not run on forks (that'd make the same mess that Dependabot makes)

Excellent catch. By default CI is disabled on forks, but I addressed that in e146f29 to be safe.

[mckib2]

@mckib2 what do you think? The notifications may be useful, assuming the issues above are taken care of.

Yes, I think this would be useful. Is it (or can it?) tag appropriate maintainers such as myself? If it's a burden in the future, we can always turn it off