fix: read credentials from gradle properties

Author: Axelen123

manager-downloader-plugin/build.gradle.kts

@@ -48,8 +48,8 @@ publishing {
             name = "GitHubPackages"
             url = uri("https://maven.pkg.github.com/revanced/revanced-manager-downloader-api")
             credentials {
-                username = System.getenv("GITHUB_ACTOR")
-                password = System.getenv("GITHUB_TOKEN")
+                username = System.getenv("GITHUB_ACTOR") ?: extra["gpr.user"] as String?
+                password = System.getenv("GITHUB_TOKEN") ?: extra["gpr.key"] as String?
             }
         }
     }
@@ -86,4 +86,4 @@ publishing {
             }
         }
     }
-}
+}