empty_env standalone test may fail depending on the environment

[Sahnvour]

I sometimes use ConEmu as my terminal emulator on windows. Under ConEmu, the empty_env test fails because the envmap is not empty.

Output added for debug:

$ zig build test-standalone -Dskip-release -Dtest-filter=empty
KV{ .key = ANSICON_DEF, .value = 7 }
KV{ .key = ANSICON, .value = 182x1000 (182x42) }
KV{ .key = ConEmuANSI, .value = ON }
test failure
...

It appears it defines these variables for compatibility with ansicon, but I don't know how it is injected into the child process.

Related documentation:
https://conemu.github.io/en/ConEmuEnvironment.html
https://conemu.github.io/en/AnsiEscapeCodes.html