GitHub Actions run on push to all branches

I found the Filter pattern cheat sheet after posting the question:

‘*’: Matches all branch and tag names that don’t contain a slash (/). The * character is a special character in YAML. When you start a pattern > with *, you must use quotes.

‘**’: Matches all branch and tag names. This is the default behavior when you don’t use a branches or tags filter.

It happened that the branch I was testing contained a slash (/), so one asterisk (*) wasn’t enough. I switched to two asterisks (**) and it works now.