Check for Windows utf-8 support in run-tests.php

[TysonAndre]

Windows terminals can have different codepages.
In some locales (especially in older OS versions),
the default codepage isn't necessarily utf-8.
Non-utf8 codepages wouldn't render this utf-8 character properly.

This is based on a similar utf-8 check in a different application : phan/phan@874e908#diff-c47b128e8e4f783d984687a8796dc74dR1464

[nikic]

I'd suggest to just drop the lightning instead...

[TysonAndre]

I'm ambivalent about keeping or removing the lightning. This just seemed like a quick fix that could get approved without objection or reverts - #3981 (comment) also brought up the --no-ansi option, #2822 (review) mentioned these objections

Ideally php would have a native cross-platform equivalent of terminal[_probably]_supports_utf8()

[nikic]

Lightning removed in 562591f.

[cmb69]

See also 55d34f7.