Use a well-defined `.invalid` top-level domain. This follows the
pattern from commit 65a3c68259 (Tests: Make CMake.FileDownload invalid
host name case more robust, 2020-01-21, v3.17.0-rc1~120^2).
Add the invalid name to `ENV{no_proxy}` because DNS lookup failure is
expected. This follows the pattern from commit c0b1f5f30c (Tests: Add
host to ENV{no_proxy} when DNS lookup failure is expected, 2021-01-29,
v3.20.0-rc1~79^2).
A more-specific error message is always displayed earlier in the
output if any real error occurred. This final summary message
is distracting to readers searching through the output for the
word "error". Simply drop it.