Bright background colors (bg_br_*() functions) are not properly closed

[rossellhayes]

The bg_br_*() family of functions do not properly close themselves:

It looks like this is because the bg_br_*() family of functions end with escape code 39, which restores the default foreground color, rather than escape code 49, which restores the default background color.

str(cli::bg_br_yellow("x"))
#> 'cli_ansi_string' chr "\033[103mx\033[39m"
str(cli::bg_yellow("x"))
#> 'cli_ansi_string' chr "\033[43mx\033[49m"

I'd be happy to submit a PR!