[libc++][format] Fixed `println.blank_line.sh.cpp` test on llvm-clang-win-x-*...

[libc++][format] Fixed `println.blank_line.sh.cpp` test on llvm-clang-win-x-* configurations (#88011)

Fix for issue:
https://github.com/llvm/llvm-project/pull/87277#issuecomment-2041864530

The test fails on the windows to linux cross builders. The proposed
resolution is to print some text. The issue is possibly due to the
original test outputting a single `\n` character.