client: Mark string as not being C format
In gettext 0.22 a string containing %b
was considered a
C format string which made it impossible for translations
to change the order of the date specifiers.
This marks it as no-c-format.
Previously discussed in Infrastructure/damned-lies#461 (closed), which led to a gettext bug fix. However apparently some strings containing %b still needs tagging since printf has added %b as a C format specifier.