use $default_branch instead of hardcoding "master"

[docwhat]

The input branch should use the actual default branch. I think you can grab this either by:

1. removing the default key in the action.yaml file
2. using $default_branch

[12rambau]

more urgent than I though as many repository are moving from master to main

[woile]

I have an open PR awaiting reviews 😅

#17

[woile]

Released

[woile]

This already solved now!