src: fix label indentation

In preparation for a cpplint version bump, move labels to be unindented.
The one space indentation we use now is flagged in cpplint 1.5.2.

Refs: https://softwareengineering.stackexchange.com/q/151806/26510

PR-URL: https://github.com/nodejs/node/pull/36213


Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>