Multiple LicenseID in SPDX

### Description

SPDX standard states that "This identifier shall be unique within the SPDX document".
https://spdx.github.io/spdx-spec/v2.3/other-licensing-information-detected/

In the attached SPDX file, some license ids are reported multiple times:
```
grep LicenseID phpwiki.spdx.txt | sort | uniq -c
1 LicenseID: LicenseRef-scancode-bsd-unmodified
1 LicenseID: LicenseRef-scancode-commercial-license
1 LicenseID: LicenseRef-scancode-free-unknown
1 LicenseID: LicenseRef-scancode-mysql-linking-exception-2018
5 LicenseID: LicenseRef-scancode-other-permissive
20 LicenseID: LicenseRef-scancode-php-2.0.2
15 LicenseID: LicenseRef-scancode-proprietary-license
3 LicenseID: LicenseRef-scancode-public-domain
23 LicenseID: LicenseRef-scancode-unknown-license-reference
3 LicenseID: LicenseRef-scancode-unknown-spdx
1 LicenseID: LicenseRef-scancode-warranty-disclaimer
```

### How To Reproduce

```
svn checkout https://svn.code.sf.net/p/phpwiki/code/trunk phpwiki
```

```
./scancode -c -l -i --license-text --spdx-tv phpwiki.spdx phpwiki
```

Resulting SPDX file:

[phpwiki.spdx.txt](https://github.com/nexB/scancode-toolkit/files/10745540/phpwiki.spdx.txt)

### System configuration

```
./scancode --version
ScanCode version: 32.0.0rc1
ScanCode Output Format version: 3.0.0
SPDX License list version: 3.19
```
Ubuntu 22.10