notes: Adding Github CI to testing documentation (#21996)

notes: Adding Github CI to testing documentation

docs/tutorial/testing-on-headless-ci.md

@@ -1,4 +1,4 @@
-# Testing on Headless CI Systems (Travis CI, Jenkins)
+# Testing on Headless CI Systems (Travis CI, Github Actions, Jenkins)
 
 Being based on Chromium, Electron requires a display driver to function.
 If Chromium can't find a display driver, Electron will fail to launch -
@@ -45,6 +45,10 @@ install:
   - Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &
 ```
 
+### Github Actions
+
+For Github Actions, a [Xvfb action is available](https://github.com/marketplace/actions/gabrielbb-xvfb-action).
+
 ### Jenkins
 
 For Jenkins, a [Xvfb plugin is available](https://wiki.jenkins-ci.org/display/JENKINS/Xvfb+Plugin).