[create-doks-with-terraform-flux] Remove redundant 'github.com' string from the `github_ssh_pub_key` variable

[v-ctiutiu]

Fixes #18.

[up-lift-dev]

This change looks like it fixed an issue for me. Thanks you @v-ctiutiu !!

Error seen in flux logs. GitRepository/flux-system.flux-system - Reconciler error auth error: knownhosts: illegal base64 data at input byte 5