login: 2fa: T874: fix PAM string generation on multiple package installations
login: 2fa: T874: fix PAM string generation on multiple package installations

Commit da535ef5 ("login: 2fa: T874: fix Google authenticator issues") used
different strings for grep and sed resulting in the same line beeing added on
every installation of the package.

This is only disturbing during development not during ISO build.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x