More robust `count_commits()`

[timvink]

Not sure what caused it, but this line:

mkdocs-git-revision-date-localized-plugin/mkdocs_git_revision_date_localized_plugin/ci.py

Line 88 in b6b0d11

refs = [x.split()[0] for x in refs]

Caused a

  File "/usr/local/lib/python3.9/site-packages/mkdocs_git_revision_date_localized_plugin/ci.py", line 88, in <listcomp>
    refs = [x.split()[0] for x in refs]
IndexError: list index out of range

[timvink]

Repo was cloned on Tekton using

/ko-app/git-init \
# other parms
    -depth="${DEPTH}"

Where default value of DEPTH is 1