tty-ask-pwd-agent: fix message forwarded to wall(1)

tty-ask-pwd-agent: fix message forwarded to wall(1)

Commit a1c111c2d12429d2 wrongly replaced '!' with ':' when the message is
forwarded to wall(1).

Indeed in this case we are not requesting the user for providing a password but
instead we are simply displaying a message to suggest starting
tty-ask-password-agent for providing the password.

(cherry picked from commit 65943cc3507bf54390d598e06df60771e913fb72)
(cherry picked from commit eb552417420fa9680b508519e926b140d5a0be25)

Gbp-Pq: Name tty-ask-pwd-agent-fix-message-forwarded-to-wall-1.patch