Negate `log.showSignature` in commits preview for `pull-request`
Negate `log.showSignature` in commits preview for `pull-request`

Fixes #1254

boris-rea/hub,boris-rea/hub,rlugojr/hub,github/hub,github/hub,cpick/hub,rlugojr/hub,tomasv/hub,boris-rea/hub,rlugojr/hub,github/hub,tomasv/hub,cpick/hub,github/hub,tomasv/hub,cpick/hub