Enable manual workflow run

[InvisibleSmiley]

Progress over at my PR #39 has stalled because the build is not passing.

I want to highlight that AFAICT all the issues appearing over there also apply to the current master state.

This PR simply allows to run the integration workflow manually, not just for PRs and master merges.
This will allow you (the maintainer) to check the result of a master build at any given time.
Once you see that there are issues on master, you can take appropriate measures to solve the issues.

[InvisibleSmiley]

Needless to say that the integration workflow build for this PR will fail, too.
It should be obvious that my change is not the cause of the issues, so just ignore it and merge manually.

[Slamdunk]

I didn't know about workflow_dispatch, thank you.

But that doesn't change much: I wouldn't have run it as I don't look after packages too often when PHP release is far.

BTW, build is now fixed again in master.

[InvisibleSmiley]

But that doesn't change much: I wouldn't have run it as I don't look after packages too often when PHP release is far.

Sure it doesn't fix anything, but you can let GitHub run all checks on master at any time with a push of a button.