Include branch in benchmarking information

[iluuu1994]

This allows https://nielsdos.github.io/php-benchmark-visualisation/ to only show commits from master (or a specific branch). Otherwise we get confusing, undulating commits from different branches, with potentially wildly different performance.

[nielsdos]

This field approach is fine for me.
The output seems wrong though, it includes stdout and stderr subfields and HEAD was not replaced with the right branch.

[iluuu1994]

I forgot to use the stdout prop. I'm not sure why the output is HEAD, it's probably because the GitHub checkout action checks out the commit instead of the branch. I might have to use the env variable then.

[staabm]

https://nielsdos.github.io/php-benchmark-visualisation/

i wonder why the graph is climbing over time.. doesnt it mean the instruction count is getting bigger and bigger and therefore php-src slower and slower?

[iluuu1994]

@staabm The first big spike is not a real performance drop. See 4ca8daf#commitcomment-111688104. Other than that, it's been pretty stable. The recent spike is caused by 766cac0, Jakub said that he will investigate this when he has the time.

The are fluctuations in the measurements that I haven't yet found the cause of. It would be nice if it was more stable, so it would be easier to point out the exact commit that causes a performance drop.