Doxygen: Fix formatting of email address

[nelliemckesson]

This section of the HTML-doxygen (see https://raspberrypi.github.io/pico-sdk-doxygen/group__pico__printf.html )

renders like this on the new version:

[nelliemckesson]

@lurch is the problem that there's no space above the first line of normal text?

[lurch]

Nope, the problem is the way the email address is getting mangled.

[nelliemckesson]

Ohhhhhh @lurch my eyes were not prepared to see that, haha