test: mark test-util-sigint-watchdog FreeBSD flaky

[Trott]

Checklist

• make -j4 test (UNIX), or vcbuild test nosign (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

test util

Description of change

Test is currently failing intermittently on FreeBSD only.

Refs: #7919

[Trott]

CI: https://ci.nodejs.org/job/node-test-pull-request/3475/

EDIT: Build failure on FreeBSD. Running this on FreeBSD is kind of important, I guess. Let's try again: https://ci.nodejs.org/job/node-test-pull-request/3476/

EDIT: Windows build failure that time. No tests on Windows seems like a bad way to go, even for a tiny change like this, so let's try another time: https://ci.nodejs.org/job/node-test-pull-request/3477/

[Trott]

CI is green.

[jasnell]

LGTM

[cjihrig]

LGTM, but perhaps we should evaluate #7933 as a fix first.

[jasnell]

Going to label this as blocked on #7933 for the time being then.

[Trott]

It is not blocked by that PR. It can land immediately. But if that PR lands first, then this becomes unnecessary.

[addaleax]

Closing this because #7933 landed. :)