GitHub Action is can't detect Functions runtime for pre-built API

I've got a GitHub Actions pipeline building my static web app and repo, resulting in a published artifact that I'd like to take to several different places. This has a pretty standard set of static files at `/`, and then a dotnet function app at `/api`.

The contents of `/api` are the result of a `dotnet publish`, so include a `host.json` and various folders containing the functions, plus a `bin` directory with the output DLLs. All this works fine when run with `func start` locally.

When I use the build task: `Azure/static-web-apps-deploy@v1` the following warning is received in the logs:

```
[WARNING] The function language could not be detected. The language will be defaulted to node.
Function Runtime Information. OS: Linux, Functions Runtime: v3, Node version: 12.X
```

As a result, the functions fail to start, returning a "Function host is not running" message. This appears to be because the deploy task is defaulting an internal setting (maybe `FUNCTIONS_WORKER_RUNTIME`) to `node` rather than `dotnet`. In Application Insights a `Microsoft.Azure.WebJobs.Script.HostInitializationException` is received, with the message "Did not find functions with language [node]." This would be consistent with the function runtime being set incorrectly.

I'm unclear whether this is an issue with Oryx failing to detect a dotnet app (look for a bin directory?) or something else. Is there an environment variable or parameter I can pass to the `Azure/static-web-apps-deploy@v1` task to make sure it sets the runtime correctly?

**To reproduce:**
- Create a sample dotnet-based Functions app
- Using GitHub Actions, restore, build, and publish it as an artifact
- Use the artifact contents as the api directory for the `Azure/static-web-apps-deploy@v1` task
- After Oryx runs, the system fails to detect the Functions language/runtime (see Actions logs)
- Attempt to hit a function endpoint, and note the "Function host is not running" message

Build info:

``` yaml
- name: Upload Static Site
uses: Azure/static-web-apps-deploy@v1
with:
azure_static_web_apps_api_token: ${{ secrets.AZSTATIC }}
repo_token: ${{ secrets.GITHUB_TOKEN }} # Used for GitHub integrations (i.e. PR comments)
action: 'upload'
app_location: 'package' # App source code path
api_location: 'package/api'
skip_app_build: true
```

It would be neat to have the Functions runtime listed in the Azure Portal.