Invalid license for PlaysetLightTest

[lexaknyazev]

• The SPDX identifier must be CC-BY-NC-SA-4.0 (note exact spelling).
• The license text must be added to the LICENSES directory.

[javagl]

The question of whether the spdx property is in fact (expected to be) an actual SPDX identifier also came up in #253 . My current understanding is that there will be spdx values that are not SPDX identifiers, but of course, if they are, then they should be spelled correctly (and the scripts could/should check for that, c.f. your comment at #254 (comment) )