Replace "git whatchanged" by "git log"

[kwin]

whatchanged is deprecated and supposed to be removed in future git versions (https://git-scm.com/docs/git-whatchanged). "log" is semantically equivalent except for different default which are anyhow overwritten in this context (skip merge commits, raw output).

This closes #1310

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[github-actions]

@kwin Please assign appropriate label to PR according to the type of change.