Possible bug in rare format cases

[Melkiades]

          for me it bugs:

[ FAIL 1 | WARN 0 | SKIP 0 | PASS 16 ]

── Error (test-count_cumulative.R:163:3): Testing label behavior when s_* forecasts label attributes ──
Error in `format_value(rawvalues(x), format = format, output = output, 
    na_str = na_str)`: Unknown format label: 'a'. Run `list_valid_format_labels()` to get a list of all available formats.

But we can fix this if it ever surfaces again or if we get there some day in the future

Originally posted by @Melkiades in #1403 (comment)