Kubernetes runner host key verification failed

I’m running Gitlab via the Gitlab-Omnibus Helm Chart

I’m attempting to build a docker image. It is a Dart project that has git dependencies. I assume I’d get the same error if it was an npm project with git dependencies as well.

Here is my .gitlab-ci.yml:

image: gitlab/dind

variables:
  REGISTRY: gitlab.company.com
  GIT_SUBMODULE_STRATEGY: recursive
  DOCKER_HOST: tcp://localhost:2375
  DOCKER_DRIVER: overlay2

services:
  - docker:dind

before_script:

    # This stuff is required to git pull from git dependency project
    - 'which ssh-agent || ( apt-get update -y && apt-get install openssh-client -y )'
    - eval $(ssh-agent -s)
    - echo "$SSH_PRIVATE_KEY" | tr -d '\r' | ssh-add - > /dev/null
    - mkdir -p ~/.ssh
    - chmod 700 ~/.ssh
    - echo "$SSH_KNOWN_HOSTS" > ~/.ssh/known_hosts
    - chmod 644 ~/.ssh/known_hosts

types:
  - analyze
  - build

analyze:
  type: analyze
  image: google/dart:1.24.3
  script:
    - dart --version
    - pub get
    - dartanalyzer --fatal-hints --fatal-warnings bin/server.dart

build_image:
  type: build
  before_script:
    # This stuff is required to git pull from git dependency project
    - 'which ssh-agent || ( apt-get update -y && apt-get install openssh-client -y )'
    - eval $(ssh-agent -s)
    - echo "$SSH_PRIVATE_KEY" | tr -d '\r' | ssh-add - > /dev/null
    - mkdir -p ~/.ssh
    - chmod 700 ~/.ssh
    - echo "$SSH_KNOWN_HOSTS" > ~/.ssh/known_hosts
    - chmod 644 ~/.ssh/known_hosts

  script:
    - docker info
    - docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN $REGISTRY
    - docker build -t $REGISTRY/group/project.

    # Push to gitlab registry
    - docker push $REGISTRY/group/project

As you can see, I’m injecting the private ssh key as recommended here, which works for the analyze job, but doesn’t work for build_image. The error I get is:

Resolving dependencies...
Git error. Command: git clone --mirror git@gitlab.company.com:group/other-project.git /root/.pub-cache/git/cache/other-project-4b9580110672b03c6de9df76806507239de7a297
Cloning into bare repository '/root/.pub-cache/git/cache/other-project-4b9580110672b03c6de9df76806507239de7a297'...
Host key verification failed.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
The command '/bin/sh -c pub get' returned a non-zero code: 1
ERROR: Job failed: error executing remote command: command terminated with non-zero exit code: Error executing in Docker Container: 1

I’m not tied to any particular approach I’m trying here, just that I want to be able to pull from another git repo on the same server.