test(env): "uv_os_getenv failed: -4071 EINVAL" #42187

Problem:
Windows CI fails since f83acfd327e3756c65f69f170055fe18a751f5f2 :
the `:grep` test greps the contents of `test/*`, which depends on
whatever is in the test files. After that commit, quickfix expands
`"$⨯"` in diagnostic_spec.lua as part of a file name, which logs an
error:

    $NVIM_LOG_FILE: D:/a/neovim/neovim/build/nvim.log_ex_cmds
    ERR 2026-09-30T17:34:03.034 T190.2776.0 os_getenv:98: uv_os_getenv(�) failed: -4071 EINVAL

Analysis:
`expand_env_esc()` has buggy logic: it reads the name bytewise (not
UTF8-aware), so expand_env("$é") looks up "\xC3".

    while (c-- > 0 && *tail != NUL && vim_isIDc((uint8_t)(*tail))) {
      *var++ = *tail++;
    }

Solution:
In the `:grep` test, grep test/functional/fixtures/bigfile.txt instead
of the entire `test/*` contents. This is faster and more predictable.

0 files changed, 0 insertions, 0 deletions