Wrong spdx detection for file generator

Some of our files contain generator of source code.

Looks like this:

```
def printHeader(dest):
year = datetime.datetime.now().year
print("# Copyright (C) %s, ACME, All Right Reserved." % year, file=dest)
print("#", file=dest)
print("# This file is subject to the terms and conditions of", file=dest)
print("# ACME Software License Agreement", file=dest)
print("# SPDX-License-Identifier: LicenseRef-ACME-Proprietary", file=dest)
print("#", file=dest)
print("# DO NOT EDIT MANUALLY", file=dest)
print("# This file was autogenerated by mighty_generate.py", file=dest)
```

The 5th line got detected by the spdx matcher, but the detected SPDX license is unknown

We do add `LicenseRef-ACME-Proprietary` in our custom SPDX license, but it is not recognised, probably the end of the line is taken as part of the full SPDX ID.