fix(day 9): use EUPLv1.2 SPDX identifier

gradle.properties

@@ -15,7 +15,7 @@ mod_id=legacy_landscape
 # The human-readable display name for the mod.
 mod_name=Legacy Landscape
 # The license of the mod. Review your options at https://choosealicense.com/. All Rights Reserved is the default.
-mod_license=EUPLv1.2
+mod_license=EUPL-1.2
 # The mod version. See https://semver.org/
 mod_version=0.1.1+1.21.1
 # The group ID for the mod. It is only important when publishing as an artifact to a Maven repository.