The composer.json package metadata file uses GPLv3 as licence tag. It seems GPL-3.0-only or GPL-3.0-or-later must now be used.

We're contaminated by helpers/namecase.php, which contains * @license http://www.gnu.org/licenses/gpl-3.0.txt. The software is described at http://dialect.ca/code/name-case/, without any hint.

As there is no specification of a "3.0 or later", it's a GPL-3.0-only.

Notification from Packagist:

The dereckson/source-templates-generator package of which you are a maintainer has
failed to update due to invalid data contained in your composer.json.
Please address this as soon as possible since the package stopped updating.

It is recommended that you use composer validate to check for errors when you
change your composer.json.

Below is the full update log which should highlight errors as
"Skipped branch ...":

[Composer\Repository\InvalidRepositoryException]: No valid composer.json was found in any branch or tag of https://github.com/dereckson/source-templates-generator, could not load a package from it.

Reading composer.json of dereckson/source-templates-generator (master)
Skipped branch master, Invalid package information:
License "GPLv3" is not a valid SPDX license identifier, see https://spdx.org/licenses/ if you use an open license.
If the software is closed-source, you may use "proprietary" as license.