Cannot detect API runtime on a Node.js project with manual extensions install

**Describe the bug**

If you try to deploy a SWA with a Node.js API where you have extensions installed manually with `func extensions install`, the deployment will fail with this message:

```
The function language detected is unsupported or invalid. The following languages are valid: node, dotnet, python. If you are not using Azure Functions, you can skip this check by removing the 'api_location' input from the GitHub workflow file.
```

You can see the error here: https://github.com/sinedied/azure-cantina/runs/2862128969?check_suite_focus=true#step:4:256

It seems that due to the fact that the project contains an `extensions.csproj` file (due to manual install), it fails to detect the runtime properly: https://github.com/sinedied/azure-cantina/tree/42370fd8de5ef540b6fef0a10754f06babe4af68/api

**Expected behavior**
The app should deploy without any issues.

**Additional context**
Note that using the automatic bundle install by adding this:
```
"extensionBundle": {
"id": "Microsoft.Azure.Functions.ExtensionBundle",
"version": "[2.*, 3.0.0)"
}
```
in my `host.json` file and removing the `extensions.csproj` file fixes the deployment, but prevents me to test locally as somehow the extensions bundle won't install using the `func` CLI (but that's a different issue).

Still it should be able to work as manual extensions install should be supported.