meta: wrap flaky test template at 80 characters

The other issue templates are wrapped at 80 characters. This
commit updates the flaky test template to be consistent.

PR-URL: https://github.com/nodejs/node/pull/33677


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>