Add %m to printf & fix CI

%m is a format specifier that prints an error string for errno. The
specifier is technically only for syslog, but musl and glibc implement
it for printf itself. Parsing for a single specifier in a single
function is error prone, especially when syslog itself is variadic.

tests/expected/bins_dynamic/stdio/printf.stdout

@@ -67,6 +67,8 @@ printed: test string, value: 11
 printed: test string 2, value: 13
 printed: test string 2, value: 13
 
+%m: Owner died
+
 C23:
 Binary %b: 100
 Binary %b alternate: 0b100