vscode: let cSpell work on commit messages, too

vscode: let cSpell work on commit messages, too

By default, the cSpell extension ignores all files under .git/. That
includes, unfortunately, COMMIT_EDITMSG, i.e. commit messages. However,
spell checking is *quite* useful when writing commit messages... And
since the user hardly ever opens any file inside .git (apart from commit
messages, the config, and sometimes interactive rebase's todo lists),
there is really not much harm in *not* ignoring .git/.

The default also ignores `node_modules/`, but that does not apply to
Git, so let's skip ignoring that, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>