Replace kotlin delegated properties in build files

Author: SgtSilvio

build.gradle.kts

@@ -77,8 +77,8 @@ gradlePlugin {
 }
 
 signing {
-    val signingKey: String? by project
-    val signingPassword: String? by project
+    val signingKey = providers.gradleProperty("signingKey").orNull
+    val signingPassword = providers.gradleProperty("signingPassword").orNull
     useInMemoryPgpKeys(signingKey, signingPassword)
 }