dgraph license reference not recognized

### Description

Dgraph license references in the Dgraph Git repository are not scanned correctly. When scanning for example https://github.com/dgraph-io/dgraph/blob/main/dgraph/cmd/root_ee.go I get the following result:

```
"path": "root_ee.go",
"type": "file",
"detected_license_expression": "polyform-free-trial-1.0.0",
"detected_license_expression_spdx": "LicenseRef-scancode-polyform-free-trial-1.0.0",
"license_detections": [
{
"license_expression": "polyform-free-trial-1.0.0",
"license_expression_spdx": "LicenseRef-scancode-polyform-free-trial-1.0.0",
"matches": [
{
"license_expression": "polyform-free-trial-1.0.0",
"license_expression_spdx": "LicenseRef-scancode-polyform-free-trial-1.0.0",
"from_file": "root_ee.go",
"start_line": 7,
"end_line": 11,
"matcher": "3-seq",
"score": 61.22,
"matched_length": 30,
"match_coverage": 61.22,
"rule_relevance": 100,
"rule_identifier": "polyform-free-trial-1.0.0_1.RULE",
"rule_url": "https://github.com/nexB/scancode-toolkit/tree/develop/src/licensedcode/data/rules/polyform-free-trial-1.0.0_1.RULE"
}
],
"identifier": "polyform_free_trial_1_0_0-5578fe3c-6f9d-f096-20fc-09d81a96b74a"
}
],
"license_clues": [],
"percentage_of_license_text": 28.04,
"scan_errors": []

```
### How To Reproduce

> Tell us how to reproduce the issue.

```
$ ./scancode -l --json-pp=/tmp/dgraph.json /tmp/root_ee.go
```

### System configuration

> For bug reports, it really helps us to know:

* What OS are you running on? Linux
* What version of scancode-toolkit was used to generate the scan file? v32.3.0-14-g65e1c2db47
* What installation method was used to install/run scancode? source