build: update shadow plugin group id (#279)

Author: ndr-brt

gradle/libs.versions.toml

@@ -91,4 +91,5 @@ dcp = ["edc-dcp-core", "edc-dcp-issuersconfig", "edc-dcp-service", "edc-dcp-sts-
     "edc-did-core", "edc-did-web", "edc-oauth2-client"]
 
 [plugins]
-shadow = { id = "com.github.johnrengelman.shadow", version = "8.1.1" }
+shadow = { id = "com.gradleup.shadow", version = "8.3.5" }
+