tests: force `dummysmtpd.py` to write its log file with '\n' on Windows
The log files were being `cat'd` in `test-patchbomb-tls.t`, and causing
gratuitous failures. Since `sys.stdout` is being written to with `str` instead
of `bytes`, use a `io.TextIOWrapper` to change the EOL, like
2924676d4728.
# Files that just need to be migrated to the formatter.
# Do not add new files here!
mercurial/cext/manifest.c
mercurial/cext/osutil.c
# Vendored code that we should never format:
syntax: glob
contrib/python-zstandard/**.c
contrib/python-zstandard/**.h
hgext/fsmonitor/pywatchman/**.c
mercurial/thirdparty/**.c
mercurial/thirdparty/**.h
mercurial/pythoncapi_compat.h