Build: maint: improve summary target output

The previous output:

• Mon Jun 13 2022 Ken Gaillot <kgaillot@redhat.com> Pacemaker-2.1.4
• Changesets: 17
• Diff: 9 files changed, 52 insertions(+), 18 deletions(-)

would now be:

• Mon Jun 13 2022 Ken Gaillot <kgaillot@redhat.com> Pacemaker-2.1.4
• 17 commits with 9 files changed, 52 insertions(+), 18 deletions(-)