Build updates

[flatcap]

I'm hoping to make a new release in a week's time.

Since the last release there have been two build changes of note:

• configure's --testing option is no longer needed
  After ./configure and make, simply make test to build and run the tests.

• idn v1 is deprecated in favour of idn2
  With no options, ./configure will enable idn2.
  --disable-idn is no longer needed.
  If you wish to build without idn2, use --disable-idn2

If you have time, please can you check the build works for you.

Thanks

@neomutt/downstream-packagers