Allow ci workflows to run on all pull_requests, rather than only those targeting main

[doug-q]

No description provided.

[aborgna-q]

I don't see why not

[doug-q]

@seyon:
The automation aspect is a safety net - guarantee code reaching main has been checked
CI gets clogged if too many branches are active at once
when I am doingstacked PRs quite often I don't expect CI to pass further up the stack - I run the CI manually when I expect it to be ok to check

Of course we should not be wasteful with CI resources, although my view is still that we should make this change.

It is very easy to enable CI on the branch in the workflow in the branch itself(i.e. apply the patch in the linked PR), perhaps we should just do that as requrired.

[doug-q]

We have agreed to instead trigger on a (yet-to-be-specified) label. I suggest run-ci. Of course, triggering on all PRs targeting main will continue.

[doug-q]

After some investigation implementing this is non-trivial. It requires disjunctive logic which has to be done through if filters on each job. I do not think the value of this justifies the effort or ongoing maintenance, so I propose to drop this. One can apply the linked patch per-branch to activate CI.