ci(translations): skip malformed .po files with a warning

Follow-up to 2b6f29a2 — my own `check=True` change correctly surfaced
that some shipped .po files (Spanish at least) are malformed and
msgfmt rejects them. Crashing the regression check on the first bad
file would hide every other language's status, so catch
CalledProcessError + RuntimeError per-file in get_counts, log a
warning, and skip the lang.

The hard-fail behavior on individual file parse failures stays in
count_translated itself (that's the bot's original ask). The caller
decides whether one bad language should torpedo the whole comparison —
and the answer is no.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>