[doctest] Update to 2.4.8

[jesse-r-s-hines]

• What does your PR fix?

  Updates doctest from 2.4.6 to 2.4.8

• Which triplets are supported/not supported? Have you updated the CI baseline?

  all, Yes

• Does your PR follow the maintainer guide?

  Yes

• If you have added/updated a port: Have you run ./vcpkg x-add-version --all and committed the result?

  Yes

[ghost]

All CLA requirements met.

[github-actions]

You have modified or added at least one portfile where deprecated functions are used.

If you feel able to do so, please consider migrating them to the new functions:
vcpkg_install_cmake -> vcpkg_cmake_install (from port vcpkg-cmake)
vcpkg_build_cmake -> vcpkg_cmake_build (from port vcpkg-cmake)
vcpkg_configure_cmake -> vcpkg_cmake_configure (Please remove the option PREFER_NINJA) (from port vcpkg-cmake)
vcpkg_fixup_cmake_targets -> vcpkg_cmake_config_fixup (from port vcpkg-cmake-config)

In the ports that use the new function, you have to add the corresponding dependencies:

{
  "name": "vcpkg-cmake",
  "host": true
},
{
  "name": "vcpkg-cmake-config",
  "host": true
}

The following files are affected:

• ports/doctest/portfile.cmake

You have modified or added at least one vcpkg.json where a "license" field is missing.

If you feel able to do so, please consider adding a "license" field to the following files:

• ports/doctest/vcpkg.json

Valid values for the license field can be found in the documentation

[ras0219-msft]

LGTM, thanks for the update!