ansible: write known_hosts entry for binary_tmp (#4051)

Add a `known_hosts` entry to allow the machines running the arm-fanned
jobs to be able to reach the `binary_tmp` git repository over ssh.

Fixes: #3680

Author: richardlau

ansible/roles/github/files/binary_tmp_known_hosts

@@ -0,0 +1 @@
+|1|RV0GwLebKrcRLruG88I/orbmg6Y=|dlBrqkgVnCQwmAOFNylzKj3M2E0= ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIDNWFPALrB+TJ1XSdEcL+0LApTQKaTWG2MDsdeMbT852

ansible/roles/github/tasks/main.yml

@@ -28,3 +28,16 @@
   become: yes
   become_user: "{{ server_user }}"
   loop: "{{ lookup('file', 'files/github_bad_hosts').splitlines() }}"
+
+# Entries in `files/binary_tmp_known_hosts` are generated via
+# `ssh-keyscan -H -t ed25519 <host>`, where `<host>` should match
+# the `TEMP_REPO_SERVER` environment variable set in Jenkins.
+- name: add binary_tmp entry in known_hosts
+  ansible.builtin.lineinfile:
+    path: "{{ user_home_dir }}/.ssh/known_hosts"
+    line: "{{ item }}"
+    state: present
+  become: yes
+  become_user: "{{ server_user }}"
+  loop: "{{ lookup('file', 'files/binary_tmp_known_hosts').splitlines() }}"
+  when: (user_home_dir.find('_arm_cross') != -1) or (user_home_dir.find('armv7l') != -1)