docs: bump bssh-keygen.1 manpage version to v2.1.2

The bssh-keygen.1 .TH header had been left at v2.1.0 since the
v2.1.0 release. Sync it with the bssh.1 / bssh-server.8 manpages
so all three report the same version.

Author: inureyes

docs/man/bssh-keygen.1

@@ -1,6 +1,6 @@
 .\" Manpage for bssh-keygen
 .\" Contact the maintainers to correct errors or typos.
-.TH BSSH-KEYGEN 1 "April 2026" "v2.1.0" "User Commands"
+.TH BSSH-KEYGEN 1 "April 2026" "v2.1.2" "User Commands"
 
 .SH NAME
 bssh-keygen \- SSH key pair generation tool