Checker seems to be returning invalid license warning

[davidperezgar]

As an user says in the forum, it giving an error with the License. Let's investigate that.

The checker seems to be returning an invalid_license warning for valid licenses. E.g., this line triggers a warning:

Main plugin file

• License: GNU General Public License (GPL) version 3

readme.txt
License: GNU General Public License (GPL) version 3
There is a suggestion to use an SPDX license identifier from here, but the above is valid according to the link.

Interestingly, this passes the checks though it is not present in the link:

Main plugin file

• License: GPLv3 or later

readme.txt
License: GPLv3 or later