ssh command Connect() error: getting SSH authentication methods: ssh: no key found - ssh

Question

I am trying to test and deploy a GitLab Project using the GitLab CI/CD. I am using a specific SSH runner for the project which runs on a virtual windows machine.
The runner recognizes the jobs.
However, when starting the pipeline, the runner stops with the following error message:
ERROR: Job failed (system failure): ssh command Connect() error: getting SSH authentication methods: ssh: no key found duration_s=9.0473929 job=3xxxxxxx4 project=4xxxxxxx0 runner=zxxxxxxj
This is my .gitlab-ci.yml file:
image: python:3.11.0-buster
stages:
- test
- deploy
cache:
paths:
- .cache/pip
- venv/
tests:
stage: test
tags:
- windows
before_script:
- Import-Module "$env:ChocolateyInstall\helpers\chocolateyProfile.psm1"
- choco install python --version=3.11 -y -f
- dir
# - choco install pip -Y
- C:\\Python311\\python.exe -m pip install --upgrade pip
- C:\\Python311\\python.exe -m pip install --upgrade setuptools
- C:\\Python311\\python.exe -m pip install -r requirements.txt
- where python
- C:\\Python311\\python.exe -m pip install virtualenv
script:
- dir
- C:\\Python311\\python.exe -m pytest src\tests\test_converter.py -p no:faulthandler
- C:\\Python311\\python.exe -m pytest src\tests\test_magicbytes.py -p no:faulthandler
# - C:\\Python311\\python.exe -m pytest src\tests\test_app.py -p no:faulthandler # collects items but does not start test
deploy-prod:
stage: deploy
tags:
- specificrunner
before_script:
- Import-Module "$env:ChocolateyInstall\helpers\chocolateyProfile.psm1"
- choco install python --version=3.11 -y -f
- dir
# - choco install pip -Y
- C:\\Python311\\python.exe -m pip install --upgrade pip
- C:\\Python311\\python.exe -m pip install --upgrade setuptools
- C:\\Python311\\python.exe -m pip install -r requirements.txt
- where python
- C:\\Python311\\python.exe -m pip install virtualenv
script:
- echo "Deployment"