Specify allowed contexts in jobs.<job_id>.services.<service_id>.image

Documentation does not mention if and which context variable can be used in `jobs.<job_id>.services.<service_id>.image`. From my tests a subset of contexts can be used and those are: `github`, `matrix`, `strategy`, `needs`, `vars` and inputs. 

Unfortunately, using `env` context is not possible. Not sure why but specifying allowed contexs in docs would be helpful when writing workflows. 

I've also changed conditional service creation example because it contained invalid example that was using `options` context which does not exist.

content/actions/using-workflows/workflow-syntax-for-github-actions.md

@@ -979,12 +979,16 @@ services:
 
 The Docker image to use as the service container to run the action. The value can be the Docker Hub image name or a registry name.
 
+> [!NOTE]
+> Usage of GitHub [contexts](https://docs.github.com/en/actions/learn-github-actions/contexts) is allowed when specyfing service image.
+> Allowed contexts are: `gitub`, `strategy`, `matrix`, `needs`, `vars` and `inputs`.
+
 If `jobs.<job_id>.services.<service_id>.image` is assigned an empty string, the service will not start. You can use this to set up conditional services, similar to the following example.
 
 ```yaml
 services:
   nginx:
-    image: {% raw %}${{ options.nginx == true && 'nginx' || '' }}{% endraw %}
+    image: {% raw %}${{ matrix.nginx_service == 'true' && 'nginx' || '' }}{% endraw %}
 ```
 
 ## `jobs.<job_id>.services.<service_id>.credentials`