[WebKit vendored code] osv-scanner fails to identify ANGLE and webrtc projects

### Summary:
`osv-scanner` fails to identify `ANGLE` and `webrtc` projects in the WebKit project while scanning for vendored code dependencies.

### Steps to Reproduce:
1. Check out WebKit (at commit ):
```
git clone https://github.com/WebKit/WebKit.git WebKit.git
```
2. Run `osv-scanner` (at commit 85563d901bec48bbe8db1242f083c42d42353ace):
```
go run ./cmd/osv-scanner/main.go -r WebKit.git/Source/ThirdParty
```

### Expected Results:
`osv-scanner` identifies `ANGLE` and `webrtc` as vendored code dependencies.

### Actual Results:
`osv-scanner` fails to identify `ANGLE` and `webrtc` as vendored code dependencies.

```
Scanning dir WebKit.git/Source/ThirdParty
Scanning directory for vendored libs: WebKit.git/Source/ThirdParty
[...]
Scanning potential vendored dir: WebKit.git/Source/ThirdParty/ANGLE
[...]
Scanning potential vendored dir: WebKit.git/Source/ThirdParty/libwebrtc
[...]
Scanning directory for vendored libs: WebKit.git/Source/ThirdParty/ANGLE/src/third_party
[...]
Scanning directory for vendored libs: WebKit.git/Source/ThirdParty/libwebrtc/Source/third_party
[...]
```

### Notes:
Both `ANGLE` and `libwebrtc` folders have their own third-party subfolders with additional vendored code dependencies.